Combined Gas Law Calculator
Solve the combined gas law P₁V₁/T₁ = P₂V₂/T₂ for the new volume of a gas.
How it works
P₁V₁ / T₁ = P₂V₂ / T₂ · V₂ = P₁ · V₁ · T₂ / (T₁ · P₂) (T in kelvin)
The combined gas law merges Boyle's, Charles's and Gay-Lussac's laws into one relationship for a fixed amount of gas: the quantity PV/T stays constant as pressure, volume and temperature all change. Rearranging solves for the final volume. Temperatures must be absolute, so Celsius entries are converted to kelvin first.
Worked example
A gas at 1 atm, 2 L and 273 K is taken to 2 atm at 273 K: V₂ = (1 × 2 × 273) ÷ (273 × 2) = 1 L — doubling the pressure at the same temperature halves the volume.
Sources: Combined gas law — Wikipedia
Frequently asked questions
Why must temperature be in kelvin?
The law depends on absolute temperature measured from absolute zero. Celsius values are converted by adding 273.15; using Celsius directly would give wrong or even negative ratios.
When do I use the combined gas law instead of Boyle's or Charles's?
Use it whenever two or more of pressure, volume and temperature change at once. If only one pair changes, the simpler single-variable laws are enough.
Does the amount of gas matter?
The combined gas law assumes a fixed number of moles. If gas is added or removed you need the full ideal gas law, PV = nRT.
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Educational estimate. Check the formula, units and significant figures for your exact case.