Ideal Gas Law Calculator
Enter any three of pressure, volume, amount and temperature. You get the fourth, with the gas constant value shown.
Fill in three of the four values and leave the one you want to find empty. The answer appears as you type, in the unit shown next to its box. R = 8.314462618 J/(mol K). Pressure and temperature are absolute inside the formula, and the page converts for you.
Worked examples
Standard conditions
1 mol at 0 C and 101.325 kPa
22.414 L
nRT / P.
Room conditions
1 mol at 25 C and 100 kPa
24.79 L
nRT / P with T = 298.15 K.
About Ideal Gas Law Calculator
The ideal gas law relates the pressure, volume, amount and temperature of a gas: the pressure times the volume equals the number of moles times the gas constant times the absolute temperature. It describes real gases well at low pressure and moderate temperature. The gas constant R is 8.314462618 joules per mole kelvin, which is also 0.082057 litre atmospheres per mole kelvin. This calculator solves for whichever of the four quantities you leave empty.
At 0 degrees Celsius and 1 atmosphere, one mole of gas occupies 22.414 litres, and at 25 degrees and 100 kilopascals it is 24.79 litres. You can type temperature in Celsius, Fahrenheit or kelvin, and the page converts to absolute temperature itself, so there is no need to add 273.15 by hand. Real gases deviate at high pressure and low temperature, where molecules take up space and attract each other.
How to use Ideal Gas Law Calculator
- Fill in three of pressure, volume, amount of gas and temperature.
- Choose the unit for each, for example kilopascals, litres or degrees Celsius.
- Leave the quantity you want to find empty.
- Read the answer and the volume, pressure and temperature in other units.
Common uses
- Chemistry problems on gas volumes and moles
- Finding the volume of gas produced in a reaction
- Working out the pressure in a sealed container when heated
- Estimating the moles of gas in a cylinder
Frequently asked questions
What is the ideal gas equation?
PV = nRT, where P is pressure, V is volume, n is moles of gas, R is the gas constant and T is the absolute temperature in kelvin.
Why must temperature be in kelvin?
The law uses absolute temperature, where zero is absolute zero. The page converts Celsius and Fahrenheit for you, so you can enter either.
What is the molar volume of a gas?
At 0 degrees Celsius and 101.325 kilopascals it is 22.414 litres per mole. At 25 degrees Celsius and 100 kilopascals it is 24.79 litres per mole.
When does the ideal gas law fail?
At high pressures and low temperatures, close to when the gas condenses. There, the volume of the molecules and the forces between them matter.