Ideal Gas Law Calculator - Solve PV = nRT for Pressure, Volume, Moles or Temperature
Ideal Gas Law Calculator
Solve PV = nRT for any variable, in the units you use
Any Unknown
Pick pressure, volume, moles or temperature and enter the other three.
Mixed Units
Each value can use its own unit; everything is converted to SI before solving.
Absolute Temperature
Celsius and Fahrenheit are converted to kelvin automatically, the most common source of mistakes.
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Calculated in your browser.
Using PV = nRT
The ideal gas law links the pressure P, volume V, amount n (in moles) and absolute temperature T of a gas through the gas constant R = 8.314462618 J/(mol·K). Temperature must be absolute: 25 °C is 298.15 K. Example: 1 mol of gas at 0 °C and 1 atm occupies 22.414 L, the classic molar volume at standard temperature and pressure.
Real gases follow the law closely at low pressure and high temperature. Near condensation or at very high pressure, molecules attract each other and take up space, and an equation such as van der Waals is more accurate. Gauge pressure from a tyre gauge must also be converted to absolute pressure by adding atmospheric pressure (about 101.3 kPa or 14.7 psi).
Key Takeaways
- Use kelvin: The law needs absolute temperature; the calculator converts for you.
- Absolute pressure: Add atmospheric pressure to gauge readings first.
- Molar volume: The result also gives litres per mole at your conditions.