Ideal Gas Law Calculator
PV = nRT connects a gas's pressure, volume, amount, and temperature. Enter any three and it solves the fourth, using R = 0.0821 L·atm/mol·K.
The ideal gas law is PV = nRT with R = 0.0821 L·atm/mol·K. Enter any three of pressure (atm), volume (L), moles, and temperature (K), leave the fourth blank, and it solves for that one. One mole at 0 °C (273.15 K) and 1 atm fills about 22.4 L.
Pressure
1.0011atm
Volume
22.4L
Amount
1mol
Temperature
273.15K
Temperature has to be in kelvin, not Celsius — add 273.15 to a Celsius reading first. Plugging in Celsius is the classic way to get a badly wrong answer here.
How it works
The ideal gas law bundles four properties of a gas into one equation: PV = nRT. Pressure times volume equals the number of moles times the gas constant times temperature.
Enter any three of pressure (atm), volume (L), moles, and temperature (K), and leave the fourth blank. The tool rearranges to isolate the missing one — pressure is nRT/V, volume is nRT/P, and so on — and skips a divide-by-zero instead of returning garbage.
The gas constant here is R = 0.0821 L·atm/mol·K, which is why pressure goes in atmospheres and volume in liters. Temperature must be in kelvin: one mole at 273.15 K and 1 atm fills about 22.4 L, the classic molar volume.
Frequently asked questions
What units does this calculator expect?
Pressure in atmospheres, volume in liters, amount in moles, and temperature in kelvin. Those match the constant R = 0.0821 L·atm/mol·K, so mixing in other units will throw the answer off.
Why does temperature have to be in kelvin?
The equation needs an absolute temperature scale where zero means no thermal energy. Celsius has an offset, so plugging it in gives wrong results — add 273.15 to a Celsius reading first.
When does the ideal gas law stop being accurate?
It assumes gas particles don't attract each other and take up no space. That holds well at everyday pressures and temperatures, but drifts off at very high pressure or very low temperature near condensation.