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The combined gas law brings Boyle's, Charles's and Gay-Lussac's laws together for a fixed amount of gas: P₁V₁/T₁ = P₂V₂/T₂. Use it when pressure and temperature both change.
A common use is converting a measured gas volume to standard temperature and pressure (STP). Enter temperatures in °C; they are converted to kelvin for you.
| Initial pressure (P₁) | 1 atm |
| Initial volume (V₁) | 500 mL |
| Initial temperature (T₁) | 27 °C |
| Final pressure (P₂) | 1 atm |
| Final temperature (T₂) | 0 °C |
| Final volume V₂ (same unit as V₁) | 455.022 |
| T₁ in kelvin | 300.15 |
| T₂ in kelvin | 273.15 |
500 mL at 27 °C becomes 455.022 mL at 0 °C.
Try this example →| Initial pressure (P₁) | 1 atm |
| Initial volume (V₁) | 1,000 mL |
| Initial temperature (T₁) | 20 °C |
| Final pressure (P₂) | 0.3 atm |
| Final temperature (T₂) | -40 °C |
| Final volume V₂ (same unit as V₁) | 2,651.09 |
| T₁ in kelvin | 293.15 |
| T₂ in kelvin | 233.15 |
At 0.3 atm and −40 °C the 1,000 L balloon grows to 2,651.09 L.
Try this example →P₁V₁/T₁ = P₂V₂/T₂ for a fixed amount of gas.
Any pressure and volume units, as long as each pair matches. Temperature must be in kelvin.
Set P₂ to 1 bar (or 1 atm) and T₂ to 0 °C.
Only the amount of gas.