The ideal gas law
PV = nRT links absolute pressure P (Pa), volume V (m³), amount of gas n (mol) and absolute temperature T (K). R is the molar gas constant, 8.314462618 J/(mol·K), which has been exact since the 2019 SI redefinition because it is the product of the Avogadro and Boltzmann constants.
Rearranged: P = nRT ÷ V, V = nRT ÷ P, n = PV ÷ RT and T = PV ÷ nR. The calculator converts your units to SI first.
| Unit | SI value |
|---|---|
| 1 atm | 101,325 Pa |
| 1 bar | 100,000 Pa |
| 1 kPa | 1,000 Pa |
| 1 L | 0.001 m³ |
| 0 °C | 273.15 K |
Worked examples
One mole at 0 °C and 1 atm: V = 1 × 8.314462618 × 273.15 ÷ 101,325 = 0.022414 m³, or 22.414 L.
Two moles at 25 °C in a 10 L container: P = 2 × 8.314462618 × 298.15 ÷ 0.010 = 495,791 Pa, about 4.89 atm.
Limits
Real gases follow PV = nRT closely at low pressure and well above their boiling point. At high pressure or near condensation, intermolecular forces and molecular size matter; use a real-gas equation such as van der Waals. Always use absolute pressure, not gauge pressure, and temperatures above absolute zero.