Combined Gas Law Calculator
Find the new volume of a gas when its pressure and temperature change — the combined gas law, which contains Boyle's, Charles's and Gay-Lussac's laws.
What a gas does when you squeeze it, heat it or both.
How the combined gas law calculator works
For a fixed amount of gas, P V ÷ T is constant, so P₁V₁ ÷ T₁ = P₂V₂ ÷ T₂. Enter the starting pressure, volume and temperature and the final pressure and temperature to get the final volume. Temperatures must be absolute: the calculator converts from °C to kelvin. Leave pressure unchanged and it is Charles's law; leave temperature unchanged and it is Boyle's.
Formula: V₂ = P₁ V₁ T₂ ÷ (P₂ T₁), T in kelvin
Worked examples
| Inputs | Final volume (V₂) | Note |
|---|---|---|
| 2 L at 101.3 kPa, 20 °C → 202.6 kPa, 50 °C | 1.1023 L | 1.10 L |
| Boyle: 2 L at 100 kPa → 400 kPa, same temperature | 0.5 L | 0.5 L |
| Charles: 1 L at 0 °C → 100 °C, same pressure | 1.3661 L | 1.366 L |
FAQFrequently asked questions
Why must temperature be in kelvin?
Because volume is proportional to absolute temperature. Doubling from 10 °C to 20 °C is not doubling the temperature; 283 K to 293 K is a 3.5% rize.
Which gas laws does this cover?
Boyle (constant T), Charles (constant P) and Gay-Lussac (constant V) are all special cases of P V ÷ T = constant.
What about the amount of gas changing?
Then use the ideal gas law P V = n R T — see the ideal-gas-law calculator.
How ideal are real gases?
Air, nitrogen and helium at ordinary pressures are within about 1% of ideal. Near liquefaction or above tens of atmospheres, deviations grow.
Where these figures come from
- IUPAC — Standard atomic weights (2021 conventional values) — the molar-mass table
- NIST — CODATA 2018 fundamental physical constants — Avogadro constant, gas constant, speed of light
- NIST Chemistry WebBook — thermochemical data
- National Institute of Standards and Technology — the US measurement and reference-data authority
Last checked: September 2026. Atomic masses are the IUPAC conventional values; constants are CODATA 2018; equations are the standard textbook forms.