Ideal Gas Law Calculator

The ideal gas law is PV = nRT. It links the pressure, volume, amount in moles and absolute temperature of a gas through the gas constant R, treating the gas as ideal.

It uses R = 0.082057 L atm per mol per kelvin. Because R is fixed in those units, any pressure in kPa, volume in m3 or temperature in Celsius is converted to atm, litres and kelvin before solving, then converted back for display.

Exactly three of the four. From any three of pressure, volume, moles and temperature the fourth is fully determined. The 'Solve for' menu marks which one is the unknown, and that row is disabled.

PV = nRT is only valid on an absolute scale where zero means zero thermal energy. Celsius inputs are converted to kelvin by adding 273.15, so 0 C becomes 273.15 K. Entering a temperature at or below absolute zero is rejected.

Pressure in atm or kPa, volume in litres or cubic metres (m3), and temperature in kelvin or Celsius. Moles are always in mol. Each row has its own unit dropdown, so you can enter kPa and Celsius together, for example.

Every result is rounded to six decimal places. That is why molar volume at STP reads 22.41387 L rather than an exact 22.414, since the underlying value carries more digits before rounding.

It assumes ideal behaviour, which is a close fit for many gases near room temperature and moderate pressure. Accuracy drops at high pressure or low temperature, where intermolecular forces and molecular volume matter and an equation like van der Waals fits better.

Pressure, volume and moles must be greater than zero and temperature must be above absolute zero, so the calculator flags any zero or negative entry rather than returning a nonsense answer.

No. The calculation runs entirely in your browser with no server round trip, so the numbers you type never leave your device.