The ideal gas law relates the pressure, volume, temperature and amount of a gas. Enter any three to find the fourth. It is accurate for most gases at everyday temperatures and pressures.
Formula
P × V = n × R × T
P is pressure in kPa, V volume in litres, n the amount in moles, T the temperature in kelvin, and R = 8.314 L·kPa/(mol·K). Convert °C to K by adding 273.15.
Worked example
One mole of gas at 0 °C (273.15 K) and 1 atm (101.325 kPa) occupies V = 1 × 8.314 × 273.15 ÷ 101.325 ≈ 22.41 L — the molar volume at standard temperature and pressure.
Frequently asked questions
What is the value of R?
R = 8.314 J/(mol·K), which equals 8.314 L·kPa/(mol·K) or 0.08206 L·atm/(mol·K). Use the version that matches your units.
When does the ideal gas law not work well?
At high pressures and low temperatures, where gas molecules are close together and attract each other. Real-gas equations such as van der Waals are used there.
Last updated · Calculations checked by automated tests· Editorial policy