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.

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 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.

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.

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.