Combined Gas Law (P₁V₁/T₁ = P₂V₂/T₂)
When n is constant, all of P, V, T can change. Solve for any one.
Result
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How to use this calculator
- Enter the 5 known values + pick which to solve.
- Read result.
About this calculator
Combined gas law: P₁V₁/T₁ = P₂V₂/T₂ for fixed amount of gas. Combines Boyle, Charles, and Gay-Lussac into one. Useful when all three properties change. Hot air balloon rising into colder, lower-pressure air: V grows (T drops slower than P drops). T must be in Kelvin.
Frequently asked
Difference from ideal gas law?+
Combined: same gas, two states. Ideal: absolute formula PV = nRT. Use combined when transforming between conditions; ideal when finding absolute properties.
When n changes?+
Use ideal gas law twice (once for each state). Or include molar fraction if mixing gases.
Kelvin?+
Always — gas laws use absolute temperature.
Real gases?+
Combined law also breaks down at high P / low T. Same caveats as ideal gas law.
Pressure units consistent?+
Yes — both sides same units (psi, atm, kPa). Same for volume.
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