Ideal Gas Law Calculator

How it is calculated

The ideal gas law links the pressure, volume, amount and temperature of a gas: P V = n R T. This tool solves it for pressure: P = n × R × T / V. Here n is the amount of gas in moles, T is the absolute temperature in kelvin, V is the volume in litres, and R = 0.0820573 L·atm/(mol·K). With these units the pressure comes out in atmospheres (atm), rounded to three decimals. Volume must be greater than zero. The law treats gas molecules as points that do not attract each other, so it works well for gases at low pressure and fairly high temperature, and loses accuracy near condensation or at very high pressure.

Common mistakes

• Entering the temperature in degrees Celsius; it must be in kelvin (add 273.15 to the Celsius value), otherwise the result is wrong.
• Entering the volume in cubic metres or millilitres when the constant expects litres.
• Using grams instead of moles; divide the mass by the molar mass first.
• Reading the answer as pascals or bar when it is in atmospheres (1 atm is about 101,325 Pa).
• Applying the law to a gas close to liquefying or at very high pressure, where real gases deviate from ideal behaviour.