Free Online Calculators

Convert length measurements between meters, feet, inches, centimeters, kilometers, and miles.

Convert temperatures between Celsius, Fahrenheit, and Kelvin using the standard scale formulas.

Convert weight and mass between kilograms, grams, pounds, ounces, and stone using exact definitions.

Convert between bytes, decimal units (KB/MB/GB/TB) and binary units (KiB/MiB/GiB/TiB) — the exact reason a '1 TB' drive shows up as ~931 GB in your OS.

Convert pressure between pascals, kilopascals, bar, psi, atmospheres, and millimeters of mercury.

Convert speed between meters per second, kilometers per hour, miles per hour, knots, and feet per second.

Convert area between square meters, square feet, square yards, acres, hectares, and square kilometers.

Convert volume between liters, milliliters, US gallons, US cups, and US fluid ounces.

Convert time between seconds, minutes, hours, days, and weeks using exact, fixed-length definitions.

Convert fuel economy between US mpg, UK mpg, liters per 100km, and km per liter — unlike most unit converters, these aren't a simple multiply.

Convert angles between degrees, radians, gradians, arcminutes, arcseconds, and full turns.

Convert energy between joules, kilojoules, calories, kilocalories (food Calories), watt-hours, kilowatt-hours, and BTU.

Convert power between watts, kilowatts, megawatts, mechanical and metric horsepower, and BTU per hour.

Calculate the exact number of days, weeks, and months between any two calendar dates.

Find the ISO 8601 week number for any date, plus the Monday-to-Sunday range of that week and how many weeks are in its ISO year.

Count the number of weekdays (Monday through Friday) between two dates, with no holiday assumptions.

Calculate exact age in years, months, and days from a birth date to today, plus total days and weeks lived.

Find which day of the week any calendar date falls on, plus its ISO weekday number and day-of-year count.

Find the Moon's phase, illumination, and days until the next new or full moon for any calendar date.

Convert an ordinal day number (1-366) and a year into the calendar date it falls on, plus its weekday and days remaining in the year.

Calculate the tip amount, total bill, and per-person share when splitting a restaurant bill evenly.

Estimate a password's entropy in bits from its length and character set, and see how that compares to common strength bands.

Find how much paint you need from the area to cover, your paint's coverage rate, and the number of coats — in metric (m²/L) or imperial (ft²/gal) units.

Compare two product sizes or package options by price per unit to find which one is actually the better deal.

Convert any whole number from 1 to 3999 into standard Roman numerals using subtractive notation.

Find bedtimes or wake-up times that align with complete 90-minute sleep cycles, from either end of the night.

Find how much stock solution and diluent to mix for a target concentration and volume, using the C1V1 = C2V2 dilution equation.

Decode a 4-band resistor's color bands into its resistance value and tolerance, using the standard EIA/IEC color code.

Convert a Unix/Linux chmod octal code like 755 into its symbolic permission notation, broken down by owner, group, and other.

Find the score you need on a final exam to reach a target overall course grade, given your current grade and the final's weight.

Work out riser height, tread depth, stringer length, and stair angle from total rise, total run, and number of steps — in metric or imperial units.

Calculate the straight-line (great-circle) distance and initial compass bearing between two latitude/longitude coordinates.

Calculate how cold the air actually feels using the National Weather Service's wind chill temperature formula.

Compare two tire sizes by their code (e.g. 225/45R17) and see the resulting change in speedometer and odometer accuracy.

Find a photo's hyperfocal distance and the near/far limits of acceptably sharp focus from focal length, aperture, subject distance, and circle of confusion.

Convert a song's tempo (BPM) into delay/echo times in milliseconds for every common note value — straight, dotted, and triplet — plus the quarter note's rate in Hz.

Calculate batting average, on-base percentage, slugging percentage, and OPS from a batter's raw counting stats.

Work out how much concrete a rectangular slab/footing or a cylindrical column/post needs, in cubic yards, cubic feet, and cubic meters, plus how many bags of pre-mix that takes.

Convert your Handicap Index into the actual Course Handicap (strokes) for a specific set of tees, using the World Handicap System formula.

Break a reported wind speed and direction into its crosswind and headwind/tailwind components relative to a runway heading.

Compare bike gears the way Sheldon Brown's gain ratio does — accounting for crank length as well as wheel size and tooth counts — in metric or imperial units.

Calculate a homebrewed beer, wine, or mead's alcohol by volume from its original and final gravity readings, using both the standard and high-gravity formulas.

Convert between an indoor rower's 500m split time and power output in watts, using the standard ergometer pace-to-power formula.

Calculate exact fret distances from the nut for any scale length, using the standard equal-temperament (12th-root-of-two) fret spacing formula luthiers use.

Calculate how hot it actually feels using the National Weather Service's heat index formula, with the NWS Caution-to-Extreme-Danger risk category.

Recover true wind speed and direction from what a sailboat's instruments actually read: apparent wind speed, apparent wind angle, and boat speed.

Turn a gauge swatch's stitch and row counts into the cast-on stitches and rows needed for a target finished size.

Scale a bread dough formula from baker's percentages — flour always counted as 100%, water/salt/yeast expressed as a percentage of that flour weight — from either a known flour weight or a target total dough weight.

Work out board feet — the standard lumber-trade volume unit — from a board's nominal thickness, width, and length, and the total for however many boards you're buying.

Estimate how long a hike will take from its distance and total elevation gain, using the classic mountaineering rule of thumb.

Calculate an arrow's kinetic energy and momentum from its weight and chronographed speed, with the commonly cited game-class energy guideline.

Check a ramp's slope, ratio, and incline angle against ADA accessibility guidelines from its rise and run, and see the minimum run needed to comply.

Calculate 3D printer filament weight and material cost from its length (or the length remaining from a known weight), diameter, and material density.

Calculate coffee extraction yield and brew strength from dose weight, beverage weight, and a refractometer TDS reading, classified against the SCA's Golden Cup Standard.

Calculate how much wax and fragrance oil a container candle needs from its volume, wax specific gravity, and fragrance load percentage.

Calculate a lead climbing fall's severity from the fall distance and rope paid out, and see where it falls on the standard risk bands.

Calculate a cricket team's Net Run Rate from runs and overs, correctly converting overs.balls notation (e.g. 45.3) to decimal overs.

Estimate density altitude from field elevation, altimeter setting, and outside air temperature using the standard FAA/AOPA pilot-training method.

Convert an HH:MM:SS:FF video timecode to a total frame count and real elapsed duration, with correct NTSC drop-frame (29.97/59.94fps) handling.

Calculate a lens's horizontal, vertical, and diagonal angle of view plus crop factor and 35mm-equivalent focal length, from focal length and sensor dimensions.

Find a roof's pitch (X:12), slope, angle, and rafter length from rise and run, with an IRC/OSHA-informed slope classification.

Estimate a displacement boat's theoretical maximum hull speed from its waterline length, using the classic 1.34√LWL rule of thumb.

Convert a stacked firewood pile's dimensions into cords, the standardized 128-cubic-foot volume unit firewood is sold by.

Calculate your Surface Air Consumption (SAC) rate from a dive's tank pressure drop, dive time, and average depth.

Calculate a stretched string's tension from its scale length, target pitch, and linear mass density — the physics behind every string-gauge chart.

Work out how many wallpaper rolls you need from your wall's width and height and the roll's dimensions, accounting for pattern repeat.

Estimate total stopping distance — reaction distance plus braking distance — from speed, driver reaction time, and road friction.

Work out how many posts, rails, and pickets a straight fence run needs from its total length, maximum post spacing, picket size, and rails per section.

Calculate how an investment grows over time with compound interest and monthly contributions, with a year-by-year growth chart.

Calculate your fixed monthly loan payment, total amount paid, and total interest from principal, rate, and term.

Calculate the fixed monthly deposit needed to reach a savings goal, given current savings and interest rate.

Calculate simple interest (I = P·r·t) and the final balance on a principal, where interest accrues only on the original amount.

Estimate how many years it takes to double an investment using the Rule of 72, compared against the exact compounding formula.

Calculate return on investment as a percentage, plus the net gain or loss, from the amount invested and the final value.

Calculate the compound annual growth rate that takes a starting value to an ending value over a number of years.

Find out how long it takes to pay off a credit card balance with a fixed monthly payment, and how much interest you'll pay along the way.

Find how many units you need to sell to cover fixed costs, from your price, variable cost per unit, and fixed costs.

Convert between markup % and margin % on a cost and selling price, and see the selling price and profit either way.

Find the final price after applying one, two, or three percentage discounts one after another — not just added together.

Solve for the future value of a lump sum today, or the present value needed to reach a future amount, given a rate and compounding schedule.

Convert a nominal annual interest rate into its true effective annual rate (APY) for a given compounding frequency.

Calculate your front-end and back-end debt-to-income ratios — the standard mortgage-qualification metrics — from income, housing cost, and other debt payments.

Calculate an asset's year-by-year depreciation and book value using the straight-line or double-declining-balance method.

Find out how many months it takes for a lower monthly payment to recoup a refinance's closing costs.

Compare a tax-free municipal bond's yield against a taxable bond's yield on an equal, after-tax basis.

Calculate a loan's loan-to-value ratio and implied equity from the property value and loan amount.

Price a fixed-rate bond from its face value, coupon rate, market yield, and years to maturity — with premium/discount status and current yield.

Calculate a fixed-rate bond's Macaulay and modified duration, and the estimated price move from a 1 percentage point change in yield.

Find a fixed-rate bond's yield to maturity from its current market price, face value, coupon rate, and years to maturity.

See how much time and interest a fixed extra monthly payment saves on a loan, compared to the standard payoff schedule.

Find the maximum loan principal a target monthly payment can afford, given the interest rate and term.

Calculate a rental property's net operating income, cap rate, cash flow, and cash-on-cash return from its price, rent, expenses, and financing.

Calculate your credit utilization ratio — total balances divided by total credit limit — and see where it falls against commonly cited credit-score guidance.

Size a trade from a fixed percentage of account equity you're willing to risk, and see the reward-to-risk ratio between your entry, stop-loss, and target prices.

Find the breakeven price, profit/loss, and max profit/loss at expiration for a long or short call or put, from the strike price, premium, and a hypothetical stock price.

Find the inflation-adjusted real interest rate from a nominal rate and an inflation rate, using the exact Fisher equation, alongside the common quick-approximation shortcut.

Value a level or growing perpetuity — an infinite stream of periodic cash flows — using the Gordon growth model, PV = C / (r − g).

Calculate a covered call's static return and if-called return, both annualized, from your stock cost basis, the strike price, and the premium received.

Work out the unearned interest rebate on a precomputed loan paid off early, using the Rule of 78s (sum-of-the-digits) method.

Find the mathematically optimal fraction of your bankroll to stake on a favorable bet, f* = p − q/b, given your win probability and the odds.

Blend a company's cost of equity and after-tax cost of debt into a single weighted average cost of capital, from the market values and rates you supply.

Find the present and future value of a series of yearly payments that increase by a fixed percentage each year — a retirement withdrawal or savings contribution that rises with inflation or a raise.

Calculate a property or business's debt service coverage ratio, DSCR = net operating income ÷ annual debt service, the metric lenders use to judge whether income alone covers loan payments.

Calculate a portfolio's Sharpe ratio, (Rp − Rf) ÷ σp, the standard measure of return earned per unit of risk taken above a risk-free rate.

Calculate a company's quick ratio (acid-test ratio) from current assets, inventory, and current liabilities — the standard short-term liquidity metric.

Break down return on equity into net profit margin, asset turnover, and financial leverage using the three-factor DuPont identity.

Estimate a monthly auto lease payment from the negotiated price, down payment, trade-in, residual value, money factor, and lease term.

Estimate a company's Altman Z-Score, the classic 1968 bankruptcy-prediction formula combining five balance-sheet and income-statement ratios into one number.

Find how many years it takes a level annual cash flow to recover an initial investment, both as a simple payback period and a discounted one.

Price a European call or put option using the Black-Scholes-Merton formula, from the spot price, strike, risk-free rate, volatility, and time to expiration.

Calculate Body Mass Index from height and weight, in metric (cm/kg) or imperial (in/lbs) units.

Estimate body fat percentage from neck, waist (and hip) circumference using the U.S. Navy circumference method, in metric (cm) or imperial (in) units.

Estimate your basal metabolic rate — the calories your body burns at rest — from age, sex, height, and weight, in metric or imperial units.

Calculate running pace (minutes per km or mile) and average speed from a distance and finish time, in metric or imperial units.

Estimate ideal body weight from height and sex using the Devine formula, in metric (cm) or imperial (in) units.

Estimate your total daily calorie needs from BMR and activity level using the standard activity-multiplier method, in metric or imperial units.

Estimate your one-rep max from a weight and rep count using the Epley and Brzycki formulas, plus a training percentage table, in kg or lbs.

Calculate your waist-to-hip ratio and see where it falls on the WHO's sex-specific health risk bands, in metric (cm) or imperial (in) units.

Calculate your waist-to-height ratio and see where it falls on the Ashwell shape chart's health risk bands, in metric (cm) or imperial (in) units.

Calculate your target heart rate training zones from age and resting heart rate using the Karvonen heart-rate-reserve method.

Calculate a powerlifting Wilks score from bodyweight and total lifted, using the published 1994 Wilks coefficient formula, in metric or imperial units.

Estimate your maximal oxygen uptake (VO2 max) from how far you can run in 12 minutes, using the Cooper test formula, in metric (km) or imperial (mi) units.

Estimate body surface area from height and weight using the Mosteller formula, the method commonly referenced for clinical drug dosing, in metric (cm/kg) or imperial (in/lbs) units.

Estimate lean body mass and implied body fat from height and weight alone using the Boer formula, in metric or imperial units.

Split a daily calorie target into grams of protein, carbs, and fat from your own target percentages.

Estimate a pregnancy due date and trimester milestones from the last menstrual period, adjusted for average cycle length.

Estimate body fat percentage from hip circumference and height alone, using the Bergman et al. Body Adiposity Index formula, in metric or imperial units.

Estimate basal metabolic rate from lean body mass using the Katch-McArdle formula, for anyone who knows their body fat percentage.

Estimate your skeletal frame size — small, medium, or large — from your height-to-wrist-circumference ratio, in metric (cm) or imperial (in) units.

Convert an A1C percentage to its estimated average blood glucose (eAG) using the ADAG study's published formula, in mg/dL and mmol/L.

Calculate FFMI and height-normalized FFMI from weight, height, and body fat percentage using the Kouri formula.

Calculate mean arterial pressure and pulse pressure from a systolic/diastolic blood pressure reading.

Estimate central (abdominal) fat distribution from waist circumference, weight, and height using Valdez's conicity index, in metric or imperial units.

Calculate Rohrer's Ponderal Index (weight ÷ height³) — a height-cubed alternative to BMI that's more reliable at very short or very tall heights — in metric or imperial units.

Predict your finish time at a new race distance from a recent result at another distance, using Peter Riegel's T2 = T1 × (D2/D1)^1.06 endurance formula.

Calculate the Body Roundness Index from waist circumference and height — an ellipse-based alternative to BMI that captures body shape, in metric (cm) or imperial (in) units.

Find X% of Y, work out what percent one number is of another, or calculate percent change between two values.

Solve ax² + bx + c = 0 with the quadratic formula, reporting the discriminant and both roots, including complex roots.

Find the greatest common divisor and least common multiple of two integers using the Euclidean algorithm.

Calculate a circle's radius, diameter, area, and circumference from either the radius or diameter.

Solve a right triangle's missing side, area, perimeter, and angles from either its two legs or its hypotenuse and one leg.

Simplify any ratio a:b to its lowest whole-number terms using the greatest common divisor.

Raise a number to any power and find its corresponding root — x^y and the y-th root of x — from the same two inputs.

Solve any triangle — not just right triangles — for its remaining sides, angles, area, and perimeter, given three sides (SSS) or two sides and the included angle (SAS).

Find the distance, midpoint, and slope between two coordinate points using the standard coordinate-geometry formulas.

Calculate the number of ordered arrangements (nPr) and unordered selections (nCr) of r items chosen from a set of n.

Find the nth term and the sum of the first n terms of an arithmetic or geometric sequence.

Find a regular polygon's interior and exterior angles, diagonal count, perimeter, apothem, and area from its number of sides and side length.

Calculate a z-score and its percentile in a normal distribution from a value, mean, and standard deviation.

Solve ax³ + bx² + cx + d = 0 for all three roots — real or complex — using the depressed cubic and Cardano's formula.

Break any whole number down into its prime factors, and see whether it's prime and how many divisors it has.

Solve two linear equations in two unknowns (a1x + b1y = c1, a2x + b2y = c2) with Cramer's rule, including the parallel-lines edge cases.

Calculate how much of a substance remains after a given time, from its half-life — for radioactive decay, drug elimination, or any first-order decay process.

Calculate the magnitude, dot product, cross product, and angle between two 2D or 3D vectors.

Solve for voltage, current, or resistance from the other two using Ohm's law, with power calculated automatically.

Find time of flight, maximum height, and horizontal range for an object launched at an angle, using standard kinematics — in metric (m/s) or imperial (ft/s) units.

Find the determinant, trace, and inverse of a 2x2 or 3x3 matrix, using the standard cofactor expansion and adjugate formulas.

Solve for pressure, volume, temperature, or moles of gas using the ideal gas law, given the other three quantities.

Solve for the angle of incidence, angle of refraction, or refractive index of either medium using Snell's law, and detect total internal reflection.

Calculate a wire's electrical resistance from its material, length, and cross-sectional area, in metric (m/mm²) or imperial (ft/in²) units.

Find the angle between a clock's hour and minute hands at any time, using the standard hands-position formula.

Calculate the arithmetic, geometric, and harmonic mean of two positive numbers — the three classical Pythagorean means.

Convert a decimal integer into binary, octal, and hexadecimal, with its exact bit length and whether it's a power of two.

Find the exact probability of rolling a specific sum, or at least/at most that sum, with any number of same-sided dice.

Generate whole-number Pythagorean triples (a² + b² = c²) from two integers using Euclid's formula, and check whether a triple is primitive.

Find the exact, at-least, and at-most probabilities for a fixed number of successes across repeated independent trials, plus the expected value and standard deviation.

Calculate the torque produced by a force applied at a distance from a pivot, at any angle, in metric (N, m) or imperial (lbf, ft) units.

Solve an oblique triangle from two angles and a side (AAS) or two sides and a non-included angle (SSA) using the Law of Sines — including the classic ambiguous case.

Compute base^exponent mod modulus using fast square-and-multiply exponentiation — the algorithm behind RSA and other public-key cryptography.

Solve for a pendulum's period, length, or the local gravitational acceleration using the small-angle simple pendulum formula.

Calculate an object's kinetic energy from its mass and velocity using KE = ½mv², in metric (kg, m/s, J) or imperial (lb, mph, ft·lbf) units.

Add, subtract, multiply, and divide two complex numbers, and find each one's magnitude and argument.

Find the arc length, sector area, and chord length of a circle's slice from its radius and central angle.

Solve three linear equations in three unknowns (a1x + b1y + c1z = d1, and so on) via Gaussian elimination, including the infinite- and no-solution cases.

Calculate the Reynolds number for a fluid flow and see whether it falls in the laminar, transitional, or turbulent range.

Calculate the electrostatic force between two point charges from their charge and separation distance, in metric or imperial distance units.

Calculate the speed of sound in dry air at a given temperature, from the standard adiabatic formula.

Solve for a lens's focal length, object distance, or image distance using 1/f = 1/do + 1/di, plus magnification and whether the image is real or virtual.

Find the centripetal force, acceleration, angular velocity, and period for an object moving at constant speed along a circular path, using F = mv²/r.

Find the equivalent resistance of up to three resistors wired in series or in parallel.

Find an RC circuit's time constant (τ = R × C) and the percent charged or discharged at a given moment, using the standard exponential charge/discharge curve.

Find the escape velocity and circular orbital velocity from a body's mass and radius, using v = √(2GM/r).

Find the observed frequency of a sound wave when the source and/or observer are moving, using the classical Doppler effect formula.

Find the probability that at least two people in a group share the same birthday — or generalize to any number of equally likely categories.

Find an ellipse's area, circumference, and eccentricity from its semi-major and semi-minor axis lengths.

Find a hyperbola's foci distance, eccentricity, asymptote slope, and semi-latus rectum from its semi-transverse and semi-conjugate axis lengths.

Calculate the restoring force and stored elastic potential energy of a stretched or compressed spring from its spring constant, in metric (N/m) or imperial (lbf/ft) units.

Solve for molarity, mass of solute, or solution volume from any two of the three, via M = (mass ÷ molar mass) ÷ volume.

Apply the impulse-momentum theorem (J = FΔt = Δp) to find an object's final momentum and velocity after a force acts on it for a given time.

Solve for orbital period, semi-major axis, or central body mass via Kepler's third law, T = 2π√(a³ ÷ GM), for a body orbiting a much larger central mass.

Find a triangle's area, perimeter, side lengths, and centroid from its three vertex coordinates using the shoelace formula.

Solve for absorbance, concentration, or path length via the Beer-Lambert law A = ε × c × l, and see the corresponding percent transmittance.

Solve for resonant frequency, inductance, or capacitance in an LC tank circuit via f = 1 ÷ (2π√(LC)), plus angular frequency and characteristic impedance.

Find any note's frequency in twelve-tone equal temperament from its pitch class and octave, with an adjustable concert-pitch reference (A4 = 440 Hz by default).

Estimate the physical length to cut a half-wave dipole or quarter-wave monopole wire antenna for a target frequency, using the free-space wavelength and an adjustable end-effect factor.

Convert between a power or voltage/amplitude ratio and decibels in either direction, and see the equivalent power and voltage ratios side by side for the same dB value.

Find the pre-game win probability the Elo rating system predicts for two players, and the resulting rating change after a win, draw, or loss.

Find the maximum deflection, bending moment, and stiffness of a cantilever or simply-supported beam under a single point load, using Euler-Bernoulli beam theory.

Find a star's distance in parsecs, light-years, and astronomical units from its measured parallax angle, using the defining relationship d(pc) = 1 / p(arcsec).

Convert between pH, pOH, hydrogen ion concentration, and hydroxide ion concentration for an aqueous solution at 25°C.

Turn your outs into an exact probability of completing your hand by the river or the next card, and compare it against the table-side 'rule of 4 and 2' shortcut.

Calculate the rotational kinetic energy and moment of inertia a spinning flywheel stores, for a disk, hoop, solid sphere, or hollow sphere shape.

Calculate a two-resistor voltage divider's output voltage, current, and power dissipation — including how much the output sags once a real load is connected.

Estimate a wind turbine's power output from blade radius, wind speed, air density, and power coefficient, and see how close that is to the theoretical Betz limit.

Calculate the overall ratio, output speed, and output torque of a two-stage compound gear train from each stage's driver and driven tooth counts.

Calculate a slender column's critical (Euler) buckling load and factor of safety against an applied load, for pinned, fixed, or free end conditions.

Calculate a buffer solution's pH from its pKa and conjugate base/acid concentrations, or solve for the base:acid ratio needed to hit a target pH.

Calculate the energy and charge stored in a capacitor from its capacitance and voltage.

Convert a tool's recommended cutting speed and chip load into spindle RPM and table feed rate for milling or drilling.

Estimate how long a battery will last at a given discharge current using Peukert's law, and see how much shorter that is than a naive capacity-divided-by-current estimate.

Calculate the energy stored in an inductor's magnetic field, and its flux linkage, from inductance and current.

Calculate an engine's static compression ratio and displacement from cylinder bore, stroke, cylinder count, and combustion chamber volume.

Calculate the terminal (maximum falling) velocity of an object from its mass, cross-sectional area, drag coefficient, and air density.

Find the angle of incidence at which reflected light becomes fully polarized, θB = arctan(n2 / n1), from the refractive indices of the two media.

Find the unknown resistance that balances a Wheatstone bridge (Rx = R2 × R3 ÷ R1) and the bridge's output voltage for a given actual Rx.

Find a blackbody's peak thermal emission wavelength from its temperature (or vice versa) via Wien's displacement law, λmax = b ÷ T.

Find the total thermal radiation power of a surface (or the temperature behind a known power), P = ε × σ × A × T⁴, from its emissivity, area, and temperature.

Find a material's stress, strain, and Young's modulus of elasticity, E = (F × L₀) ÷ (A × ΔL), from a tension/compression test's force, cross-section, length, and extension.

Find how much liquid is in a horizontal cylindrical tank (propane, fuel, water, septic) from its diameter, length, and fill height — accounting for the tank's curved cross-section.

Calculate a coil's self-inductance from its number of turns, cross-sectional area, and length — the standard long-solenoid approximation.

Calculate the magnetic force between two parallel current-carrying wires — the same relationship that historically defined the ampere.

Calculate the belt length needed for a pulley drive (open or crossed) and the resulting speed ratio and driven-pulley RPM.

Calculate the output frequency, period, and duty cycle of a 555 timer wired in astable (free-running oscillator) mode from its R1, R2, and C values.

Find out whether an object floats or sinks in a fluid, the buoyant force and net force involved, and — if it floats — what fraction of it stays submerged.

Calculate the fluid pressure at a given depth — gauge pressure and absolute pressure in kPa, atm, and psi.

Estimate how long a cylindrical tank takes to drain through a hole in its base, using Torricelli's law.

Check whether an op-amp's slew rate can support a target output frequency and amplitude without distortion.

Find a resistor-inductor circuit's time constant (τ = L ÷ R) and the percent of final current reached (or remaining) at a given moment.

Estimate a room's reverberation time (RT60) from its volume, surface area, and average sound absorption coefficient, using Sabine's equation.

Find the Schwarzschild radius — the black-hole event-horizon radius — for any mass, Rs = 2GM/c², and see how it compares to the body's actual radius.

Find the resonant frequency of a cavity-and-neck resonator (a bottle, a speaker port, a tuned enclosure) from its neck dimensions and cavity volume.

Find the diffraction-limited angular resolution of a lens, telescope, or microscope from its aperture diameter and light wavelength, using θ = 1.22λ/D.

Calculate how long one full back-and-forth swing takes for a mass on an ideal spring, from its mass and the spring's stiffness.

Calculate fluid flow rate through a Venturi meter from pipe and throat diameter, the measured pressure drop, and fluid density.

Find the head loss and pressure drop a fluid loses to friction flowing through a straight pipe, h_f = f × (L/D) × (v²/2g), from the Darcy friction factor, pipe geometry, and flow velocity.

Find the critical angle above which light hitting a boundary undergoes total internal reflection, θc = arcsin(n2 / n1), from the refractive indices of the two media.

Find an ideal transformer's secondary voltage and current from its primary winding's voltage, current, and the turns ratio between the two windings.

Find a cross-section's area moment of inertia and radius of gyration for a rectangle, solid or hollow circle, or triangle — the I this site's Beam Deflection and Column Buckling calculators take as a direct input.

Find an optical fiber's numerical aperture and light-acceptance cone angle from its core and cladding refractive indices, NA = √(n1² − n2²).

Find the angle at which a diffraction grating sends a given order of light, d·sin(θm) = m·λ, from the grating's lines-per-millimeter rating, the light's wavelength, and the order number.

Calculate a confidence interval for a population mean from a sample's mean, standard deviation, and size, at any confidence level — not just the usual 90/95/99% presets.

Calculate a reaction's rate constant at two temperatures, and how much faster it runs between them, from its activation energy via the Arrhenius equation k = A·e^(−Ea/RT).

Calculate the volumetric flow rate of a laminar, viscous fluid flow through a pipe via the Hagen-Poiseuille equation, Q = π·ΔP·r⁴ ÷ (8·μ·L), from pipe diameter, length, pressure drop, and fluid viscosity.

Calculate a circular shaft's angle of twist and peak shear stress under an applied torque, θ = T·L ÷ (J·G), for a solid or hollow cross-section, plus its factor of safety against an allowable shear stress.

Calculate a series RLC circuit's resonant frequency, quality factor (Q), -3dB bandwidth, and damping ratio from its resistance, inductance, and capacitance.

Calculate a parallel RLC (tank circuit) resonant frequency, quality factor (Q), and -3dB bandwidth from its resistance, inductance, and capacitance.

Find time of flight, range, and horizontal distance for an object launched at an angle onto an upward or downward sloping incline, generalizing flat-ground projectile motion.

Calculate a parallel-plate capacitor's capacitance, stored charge and energy, and the electric field between the plates, from plate area, separation, and dielectric.

Calculate a rocket's total velocity change (delta-v) from its initial and final mass and engine specific impulse, Δv = Isp·g₀·ln(m₀/m₁).

Calculate a photoelectron's maximum kinetic energy and ejection speed from incident light's wavelength and a material's work function, KE_max = hc/λ − φ.

Calculate an ideal op-amp circuit's closed-loop gain and output voltage for the standard inverting (Av = -Rf/Rin) or non-inverting (Av = 1 + Rf/Rin) feedback topology, plus the gain in dB.

Calculate the terminal settling velocity of a small spherical particle falling through a viscous fluid using Stokes' law, v = (2/9)·(ρp−ρf)·g·r²/μ, plus the particle Reynolds number that checks whether the law's low-Reynolds-number assumption actually holds.

Calculate the clamp force (preload) a tightening torque produces in a threaded fastener, F = T ÷ (K·D), and the resulting axial stress in the bolt shank, using the standard nut-factor torque-tension equation.

Calculate the mutual gravitational attraction between two masses, F = G·m₁·m₂/r², using Newton's law of universal gravitation.

Calculate the ideal frictionless banking angle for a curve at a given speed and radius, tan(θ) = v²/(r·g), the physics behind banked roads, race tracks, and railways.

Find the equivalent spring constant of up to three springs wired in series or in parallel.

Find how much a dissolved solute shifts a solvent's freezing or boiling point, using the colligative-property formula ΔT = i × K × m.

Find a light source's redshift (z) and the line-of-sight velocity it implies from an emitted and observed wavelength, using the relativistic Doppler formula.

Find a thin lens's focal length and optical power from the refractive index and radii of curvature of its two surfaces, 1/f = (n-1)(1/R1 - 1/R2).

Solve for pressure, volume, or temperature at one of two gas states using the combined gas law, P1V1/T1 = P2V2/T2, given the other five quantities.

Find the new rotational speed and kinetic energy change when a spinning object's moment of inertia changes with no external torque, like a figure skater pulling in their arms.

Size the current-limiting resistor for one or more LEDs in series, with the nearest standard (E12) resistor value and power dissipation.

Find the minimum survey sample size needed to estimate a population proportion within a target margin of error and confidence level.

Find the magnetic force on a charged particle moving through a magnetic field, F = qvB sin(θ), from its charge, speed, field strength, and angle.

Find the drag force a moving object experiences through air or another fluid, F = ½ × Cd × ρ × A × v², from its speed, frontal area, drag coefficient, and fluid density.

Compute a photo's Exposure Value from aperture, shutter speed, and ISO, and find the shutter speed needed at a different aperture/ISO to keep the same exposure.

Find the output force and piston travel of a two-piston hydraulic press or jack from Pascal's law, F2 = F1 × (d2/d1)².

Estimate how a substance's vapor pressure shifts between two temperatures from its molar latent heat of vaporization, via the integrated Clausius-Clapeyron equation.

Find the modular inverse of an integer — the value x such that a·x ≡ 1 (mod m) — using the extended Euclidean algorithm.

Calculate the heat energy needed to raise or lower a substance's temperature from its mass, specific heat capacity, and temperature change — in joules, kJ, kWh, and kcal.

Find the true probability of a condition after a positive or negative test result, given how common the condition is and the test's true- and false-positive rates — Bayes' theorem applied to diagnostic testing.

Find φ(n), the count of integers from 1 to n that are coprime to n, along with n's distinct prime factors.

Compare how fast two gases effuse or diffuse from their molar masses, using Graham's law: rate ∝ 1/√(molar mass).

Convert a three-resistor Wye (star) network to its electrically equivalent Delta network, or Delta to Wye.