Charles's Law Calculator
Find a gas's new volume when temperature changes.
Results update as you type.
How it works
Charles's law describes how a gas expands when heated and contracts when cooled, and this calculator applies it to find a gas's new volume after a temperature change at constant pressure. You enter the starting volume and temperature and the new temperature, and it returns the final volume. The law states that, for a fixed quantity of gas held at constant pressure, volume is directly proportional to absolute temperature, so if you double the temperature in kelvin the volume doubles too. The crucial requirement is that temperatures be expressed in kelvin, not Celsius or Fahrenheit, because the proportionality only works when measured from absolute zero; using Celsius would give badly wrong answers. Charles's law explains everyday phenomena such as a balloon shrinking in cold air and expanding in warmth, hot-air balloons rising because heated air is less dense, and the pressure warnings on aerosol cans. It is one of the fundamental gas laws that together form the combined and ideal gas laws, and chemistry students study it as a building block for understanding gas behaviour. Enter the initial volume, initial temperature, and final temperature in kelvin to see the resulting volume.
V₁ / T₁ = V₂ / T₂
Charles's law says that at constant pressure the volume of a fixed amount of gas is directly proportional to its absolute temperature, so the ratio of volume to temperature stays constant. Rearranging gives the new volume as the initial volume multiplied by the ratio of the final to the initial temperature. Temperatures must be in kelvin, the absolute scale, because the proportionality only holds when temperature is measured from absolute zero.
Source:Gas laws (Charles's law)
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Worked example
How to use this calculator
- 1
Enter your values
Enter initial volume (v₁), initial temperature (t₁) and final temperature (t₂).
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Final volume (V₂) updates instantly as you type — no button to press.
Frequently asked questions
What is Charles's law?
Charles's law states that the volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. In other words, heating a gas makes it expand and cooling it makes it contract, in exact proportion to the temperature measured in kelvin. It is one of the fundamental gas laws and a special case of the more general combined and ideal gas laws.
Why must temperature be in kelvin?
The direct proportionality between volume and temperature only holds when temperature is measured from absolute zero, which is what the kelvin scale does. Celsius and Fahrenheit have arbitrary zero points, so using them would break the proportionality and give incorrect results. To convert, add 273.15 to a Celsius temperature to get kelvin before applying Charles's law.
What happens to gas volume when it is cooled?
Cooling a gas at constant pressure reduces its volume in proportion to the drop in absolute temperature. Halving the temperature in kelvin halves the volume. This is why a balloon shrinks when taken into cold air and why gases contract dramatically near very low temperatures. The relationship is linear all the way down toward absolute zero, where the volume would theoretically reach zero.
What are real-world examples of Charles's law?
Hot-air balloons rise because heating the air inside expands it, making it less dense than the surrounding air. A partially inflated balloon shrinks in a freezer and expands in the sun. Bread and cakes rise as trapped gases expand when heated. Car tyres and aerosol cans are affected by temperature changes too. All of these reflect the volume-temperature proportionality of Charles's law.
How does Charles's law relate to the other gas laws?
Charles's law is one of three simple gas laws, alongside Boyle's law, which links pressure and volume, and Gay-Lussac's law, which links pressure and temperature. Combining all three gives the combined gas law, and adding the amount of gas produces the ideal gas law. Each simple law holds one or more variables constant while relating the others.