The Ideal Gas Law

This ideal gas law calculator solves PV = nRT for any one of pressure, volume, moles, or temperature using R = 0.08206 L·atm/(mol·K). Enter three quantities, pick the unknown, and the fourth is computed by rearrangement.

Unit Discipline

The constant fixes the unit system: atmospheres, liters, moles, and kelvin. Temperature must be absolute — room temperature is 298.15 K, not 25 — otherwise every result is off by a factor tied to the 273-degree offset.

When Real Gases Deviate

At high pressure or near the boiling point, intermolecular forces and molecular volume become significant and real gases depart from ideal behavior. Van der Waals corrections restore accuracy where this simple model fails.