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Charles Law calculator
Charles's law says that at constant pressure the volume of a gas is proportional to its absolute temperature. Solve for any unknown volume or temperature.
Charles Law calculatorCharles' Law
V₁/T₁ = V₂/T₂ · Isobaric Gas Behavior Engine
Charles' Law requires absolute temperature (Kelvin). Celsius/Fahrenheit inputs are auto-converted.
Charles's law captures how gases breathe with heat: at constant pressure, a gas's volume grows in direct proportion to its absolute temperature. This calculator solves the V1/T1 = V2/T2 relationship for whichever value is missing.
How to use this calculator
- Enter any three of: initial volume, initial temperature, final volume, final temperature.
- Use kelvin for temperatures (the calculator converts if Celsius is selected).
- Press calculate to see the missing value.
Kelvin is not optional
The proportion works only with absolute temperature. Doubling from 20 °C to 40 °C is not doubling at all; in kelvin it is 293 K to 313 K, a rise of only about 7%. Most wrong answers with this law are unit errors wearing a disguise.
Frequently asked questions
What is Charles's law formula?
V1/T1 = V2/T2, with T in kelvin, at constant pressure and amount of gas.
How do I convert Celsius to kelvin?
Add 273.15. So 25 °C is 298.15 K. Always convert before using any gas law that involves a temperature ratio.
Where does Charles's law show up in real life?
Hot-air balloons (heated air expands and lifts), a balloon shrinking in a cold car overnight, and tyre pressures drifting with the seasons.