Charles's Law Calculator (V1/T1 = V2/T2)
Charles's law says a gas expands when heated at constant pressure. Choose the value to find, enter the other three, and the calculator converts Celsius to kelvin for you.
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Formula
V1 ÷ T1 = V2 ÷ T2 (constant pressure and amount of gas, T in kelvin)
- Solve for each unknown:
V2 = V1 × T2 ÷ T1,T2 = T1 × V2 ÷ V1,V1 = V2 × T1 ÷ T2,T1 = T2 × V1 ÷ V2. - Kelvin = Celsius + 273.15. A temperature of 0 K gives a division by zero and anything below it is rejected.
- 1 L = 1000 mL = 0.001 m³; the units cancel in the ratio.
Worked example
A 2 L balloon at 300 K is warmed to 350 K at constant pressure.
- V2 = V1 × T2 ÷ T1 = 2 × 350 ÷ 300
- V2 = 2.333 L, an increase of 16.7%.
- Volume per kelvin is 2 ÷ 300 = 0.006667 L/K on both sides.
Frequently asked questions
What is Charles's law?
At constant pressure, the volume of a fixed amount of gas is directly proportional to its absolute temperature: V1 ÷ T1 = V2 ÷ T2. Heat a gas and it expands; cool it and it contracts.
Why do I have to use kelvin?
Volume would reach zero at absolute zero, 0 K or -273.15 °C, so proportionality only holds on the kelvin scale. Using Celsius directly gives wrong answers: 20 °C is 293.15 K, not 20.
How do I find the final volume when a gas is heated?
Use V2 = V1 × T2 ÷ T1. A balloon of 2 L at 300 K warmed to 350 K has V2 = 2 × 350 ÷ 300 = 2.333 L, an increase of 16.7%.
How do I find the temperature needed for a given volume?
Use T2 = T1 × V2 ÷ V1. A 3 L sample at 20 °C (293.15 K) that must reach 4.5 L needs T2 = 293.15 × 4.5 ÷ 3 = 439.725 K, which is 166.575 °C.
Does Charles's law work for a sealed rigid container?
No. It needs constant pressure, so the container must be free to expand, like a balloon or a piston. In a rigid container volume is fixed and pressure rises with temperature instead, which is Gay-Lussac's law.