Ideal Gas Law Calculator (PV = nRT)
The number of moles of a gas from its pressure, volume and temperature.
Result
Amount (moles)
0.9994
How it works
The ideal gas law ties together the four properties of a gas: PV = nRT. Rearranged for the amount of substance, n = PV ÷ RT, with R = 0.0821 L·atm/mol·K in the units this calculator uses. Units are where most errors happen. Pressure must be in atmospheres, volume in litres, and temperature in kelvin — never in Celsius. Forgetting to add 273.15 is the classic mistake, and it does not merely shift the answer, it wrecks it: 25 °C entered as 25 instead of 298 K gives a result twelve times too large. The law describes an idealisation: molecules with no volume and no attraction between them. Real gases follow it closely at ordinary pressures and temperatures, and depart from it near condensation — at high pressure or low temperature, where molecules are crowded enough for their own size and mutual attraction to matter.
Advertisement
Frequently asked questions
What units does it need?
Atmospheres, litres and kelvin with R = 0.0821; remember to convert °C to K by adding 273.15.
When does it break down?
At very high pressure or very low temperature real gases deviate from ideal behaviour.
What is the molar volume at standard conditions?
About 22.4 litres per mole at 0 °C and 1 atm. That single figure lets you convert gas volumes to moles in your head for many textbook problems.
Advertisement