Charles's Law Calculator (Volume–Temperature)
Use Charles's law V₁/T₁ = V₂/T₂ to find a gas's new volume when its temperature changes at constant pressure.
How it works
V₁ / T₁ = V₂ / T₂ · V₂ = V₁ × T₂ / T₁ (constant pressure, T in kelvin)
Charles's law states that at constant pressure the volume of a fixed amount of gas is directly proportional to its absolute temperature. Heat the gas and it expands in step with the kelvin temperature; cool it and it contracts. Temperatures must be absolute, so Celsius entries are converted to kelvin by adding 273.15 before the ratio is taken.
Worked example
A gas of 2 L at 300 K heated to 600 K at constant pressure expands to V₂ = 2 × 600 ÷ 300 = 4 L — doubling the absolute temperature doubles the volume.
Sources: Charles's law — Wikipedia
Frequently asked questions
Why must temperature be in kelvin?
The proportionality is with absolute temperature measured from absolute zero. Using Celsius would break the ratio — a gas at 0 °C does not have zero volume, but the law behaves correctly once 273.15 is added to reach kelvin.
What stays constant in Charles's law?
Pressure and the amount of gas. Only volume and temperature change, which is why a balloon swells in warm air and shrinks in the cold at roughly constant atmospheric pressure.
What if pressure changes too?
Then use the combined gas law, P₁V₁/T₁ = P₂V₂/T₂, which handles simultaneous changes in pressure, volume and temperature.
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Educational estimate. Check the formula, units and significant figures for your exact case.