Combined Gas Law Calculator

P₁V₁/T₁ = P₂V₂/T₂, with kelvin handled for you.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Initial pressure

atm

Initial volume

Initial temperature

°C

Final pressure

atm

Final temperature

°C

Final volume (L)

2 L → 1 L

Initial volume2 L

Final volume1 L

Initial pressure1 atm

Final pressure2 atm

Initial temperature298.15 K

Final temperature298.15 K

P₁V₁/T₁ = P₂V₂/T₂. Boyle, Charles and Gay-Lussac are all this equation with one variable held constant, which is why learning three laws is unnecessary. Temperatures convert to kelvin before anything else happens, because the relationship is proportional to absolute temperature.

How the Combined Gas Law Calculator works

Boyle, Charles and Gay-Lussac are all this one equation with a variable held constant, which is why learning three laws is unnecessary. Temperatures convert to kelvin before anything else happens, because the relationship is proportional to absolute temperature.

Also known as: p1v1t1 p2v2t2 calculator · gas law calculator · combined gas law formula · how to use the combined gas law

Where to go next

The Combined Gas Law question rarely arrives on its own. These are the ones that usually come with it:

Boyle's Law Calculator — PV constant: halve the volume, double the pressure.
Charles's Law Calculator — V/T constant, and only in kelvin.
Ideal Gas Law Calculator — PV = nRT, solving for whichever term is missing.
Molar Volume Calculator — STP is ambiguous — 22.414 and 22.711 are both correct.

Sources

Frequently asked questions

What is the combined gas law?

P₁V₁/T₁ = P₂V₂/T₂. It relates a fixed amount of gas between two states, and reduces to Boyle, Charles or Gay-Lussac when one variable is held constant.

Why must temperature be in kelvin?

Because the relationship is proportional to absolute temperature. Using Celsius makes 0° into zero, implying a gas has no volume at freezing point, and the error looks plausible rather than obvious.

What is the difference from the ideal gas law?

The combined law compares two states of the same gas sample and needs no gas constant. The ideal gas law, PV = nRT, describes one state and requires the amount in moles.

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