Charles's Law Calculator
Solve for any one of V₁, T₁, V₂, or T₂ using Charles's Law, V₁/T₁ = V₂/T₂, with temperatures in kelvin.
Leave exactly one field blank and the calculator finds it from V₁/T₁ = V₂/T₂. Temperatures must be in kelvin, since the ratio only holds on an absolute scale.
Volume 1
2
Temperature 1
300K
Volume 2
3
Temperature 2
450K
How it works
Charles's Law describes how a gas expands when you heat it at constant pressure: volume is directly proportional to absolute temperature. Double the kelvin temperature and the volume doubles. As an equation, V₁/T₁ = V₂/T₂ — the volume-to-temperature ratio stays fixed.
Leave one box blank and the calculator solves for it. Warm 2 liters of gas from 300 K to 450 K and it works out the new volume of 3 liters. The same rearrangement finds a missing temperature just as easily.
The catch is that temperature has to be in kelvin, not Celsius or Fahrenheit. The law is built on an absolute scale where zero really means no thermal motion, so the ratios only work from there. To convert, add 273.15 to a Celsius reading before entering it — and the calculator will flag any temperature at or below absolute zero.
Frequently asked questions
Why must temperature be in kelvin?
Because Charles's Law is a proportion, and it only holds on an absolute scale. Zero kelvin is true zero thermal energy, so ratios like V/T mean something there. Celsius and Fahrenheit have arbitrary zeros, which would give nonsense answers.
How do I convert Celsius to kelvin?
Add 273.15. Room temperature of 25 °C becomes 298.15 K, and water's boiling point of 100 °C becomes 373.15 K. Do that conversion before typing the values in.
What stays constant in Charles's Law?
Pressure and the amount of gas. The law only applies when those two are held fixed and only temperature and volume change. If pressure also varies, reach for the combined gas law or the ideal gas law.