Ideal Gas Law Calculator (PV = nRT)
Solve the ideal gas law PV = nRT for pressure, volume, moles or temperature. Enter the three you know and pick the one to find.
Quick answer: The ideal gas law is PV = nRT, with R = 0.08206 L·atm/(mol·K). For 1 mol of gas at 1 atm and 273.15 K (STP), V = nRT ÷ P = (1 × 0.08206 × 273.15) ÷ 1 = 22.41 L.
Uses R = 0.08206 L·atm/(mol·K), so pressure in atm, volume in litres, temperature in kelvin. (°C + 273.15 = K.)
The ideal gas law ties together the four state variables of a gas — pressure, volume, amount and temperature — through the gas constant R. It's an approximation that holds well for real gases at ordinary conditions and is the workhorse relation of gas problems in chemistry and physics.
The equation and rearrangements
PV = nRT · R = 0.08206 L·atm/(mol·K)
P = nRT ÷ V · V = nRT ÷ P · n = PV ÷ RT · T = PV ÷ nR
P = nRT ÷ V · V = nRT ÷ P · n = PV ÷ RT · T = PV ÷ nR
Worked example
How much volume does 2 mol of gas occupy at 1.5 atm and 300 K? V = nRT ÷ P = (2 × 0.08206 × 300) ÷ 1.5 = 32.82 L.
Frequently asked questions
What is the ideal gas law?
PV = nRT, relating pressure, volume, moles and temperature through the gas constant R.
Which value of R does this use?
R = 0.08206 L·atm/(mol·K), so enter pressure in atm, volume in litres and temperature in kelvin.
How do I convert Celsius to kelvin?
Add 273.15. For example 25 °C = 298.15 K. Temperature must be in kelvin for the gas law.
What volume is one mole at STP?
At 0 °C (273.15 K) and 1 atm, one mole of an ideal gas occupies about 22.41 litres.
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