Combined Gas Law: Final Pressure Calculator
Solve the combined gas law P₁V₁/T₁ = P₂V₂/T₂ for the final pressure P₂ after a volume and temperature change.
How it works
P₁V₁ ÷ T₁ = P₂V₂ ÷ T₂ · P₂ = P₁·V₁·T₂ ÷ (T₁·V₂) · temperatures in kelvin
The combined gas law links pressure, volume and temperature for a fixed amount of gas. Solving it for the final pressure gives P₂ = P₁V₁T₂ ÷ (T₁V₂): compressing the gas (smaller V₂) or heating it (larger T₂) both raise the pressure. Every temperature must be in kelvin, since the law relies on an absolute scale.
Worked example
A gas at 1 atm and 2 L, held at 273.15 K, is compressed to 1 L and warmed to 300 K. Then P₂ = (1 × 2 × 300) ÷ (273.15 × 1) = 2.197 atm — roughly double, from halving the volume plus the modest heating.
Sources: Combined gas law — Wikipedia
Frequently asked questions
Do the pressure and volume units matter?
They just need to be consistent between the initial and final states — the ratio cancels the units. Temperature, however, must be absolute (kelvin).
What stays constant here?
The amount of gas (moles). The combined gas law applies to a sealed sample; if gas is added or removed you need the full ideal gas law instead.
How do I get kelvin from Celsius?
Add 273.15 to the Celsius temperature. For example 27 °C is 300.15 K.
Related calculators
Educational estimate. Check the formula, units and significant figures for your exact case.