Solve for pressure, volume, moles or temperature with the ideal gas equation PV = nRT, in the units you choose.
mol
Enter the values to see the result here.
Formula
PV=nRT
with P in pascals, V in cubic metres, n in moles, T in kelvin and R=8.314462618Jmol−1K−1. Rearranged: V=nRT/P, P=nRT/V, n=PV/RT and T=PV/nR.
Worked example
What volume does 1 mol of gas occupy at 0 °C and 1 atm?
T=0+273.15=273.15 K and P=101325 Pa.
V=nRT/P=1×8.31446×273.15/101325=0.022414m3.
That is 22.414 L, the molar volume at standard temperature and pressure.
At 25 °C the same mole occupies 24.465 L.
Common mistakes
Using Celsius directly in the equation. Convert to kelvin first.
Mixing pressure units, for example atm with R in kPa units. Choose the unit and let the tool convert.
Reading cm³ as litres. One litre is 1000 cm³.
Applying the law to a liquid, a near-condensing vapour or a gas at very high pressure.
Frequently asked questions
Why must the temperature be in kelvin?
The law relates pressure and volume to the absolute temperature. A Celsius or Fahrenheit value can be zero or negative while the gas still has energy, so the equation only works from absolute zero. The tool converts for you.
What value of R is used?
R = 8.314462618 J/(mol·K), which equals 0.082057 L·atm/(mol·K). The tool converts every unit to pascals, cubic metres and kelvin first, so the unit of R never has to match your inputs.
When does the ideal gas law fail?
At high pressure or low temperature, where molecules take up real space and attract each other. Near condensation, use the van der Waals equation or a compressibility factor.