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Ideal Gas Law Calculator (PV = nRT)

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

Pressure (P)
101.325 kPa
Volume (V)
22.414 L
Temperature (T)
273.15 K
Amount of substance (n)
1 mol

How it works

The ideal gas law relates a gas's pressure, volume, temperature, and amount of substance as PV = nRT, where R is the universal gas constant, 8.314462618 J/(mol·K). Entering pressure in kilopascals and volume in liters lets that same numeric value of R be used directly, since 1 kPa·L equals exactly 1 joule.

Pick which quantity to solve for; the calculator rearranges the same identity to find it from the other three (e.g. V = nRT ÷ P when solving for volume) and ignores whatever placeholder value is in the field you're solving for.

Temperature must be entered in Kelvin, an absolute scale where 0 means no molecular kinetic energy at all — the law is derived from that assumption, so a Celsius or Fahrenheit reading would make the relationship nonlinear. The defaults (101.325 kPa, 273.15 K, 1 mol) solve to 22.414 L — the textbook molar volume of an ideal gas at standard temperature and pressure.

FAQ

Why does this only work for an 'ideal' gas?

The ideal gas law assumes gas molecules take up no volume themselves and don't interact with each other, which is a good approximation for most real gases at ordinary pressures and temperatures. It becomes less accurate at very high pressure or very low (near-condensing) temperature, where real molecular size and intermolecular forces start to matter.

Why kilopascals and liters instead of pascals and cubic meters?

The gas constant R = 8.314462618 J/(mol·K) is defined in SI base units (pascals and cubic meters), but 1 kPa·L works out to exactly the same 1 joule, so using kilopascals and liters avoids awkward factors of 1000 without changing the math or the constant used.

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