Find a gas’s new volume when its temperature changes, at constant pressure, using Charles’s law.
How it works
Charles’s law states V₁ ÷ T₁ = V₂ ÷ T₂, with temperature in kelvin. A 2-liter gas sample at 300 K expands to about 2.33 liters when heated to 350 K.
What this does not include
This is distinct from this site’s Boyle’s law calculator, which holds temperature constant and relates pressure and volume instead. Charles’s law specifically requires temperature in kelvin, since the proportionality depends on distance from absolute zero.
How to use this calculator
- Enter the initial volume.
- Enter the initial temperature in kelvin.
- Enter the final temperature in kelvin.
A worked example
A gas at 2 L, 300 K, heated to 350 K at constant pressure: new volume = V1×(T2/T1) = 2×(350/300) = 2.3333 L.
5 L at 273.15 K (0°C), heated to 373.15 K (100°C): new volume = 6.8305 L.
What the variables mean
| Variable | Meaning |
|---|---|
| V1, T1 | Initial volume and temperature (Kelvin) |
| T2 | New temperature |
Edge cases worth knowing
Temperatures must be in Kelvin, not Celsius or Fahrenheit. Charles’s Law is a proportional relationship anchored at absolute zero, so using Celsius directly would give a wrong result — this is why the second example explicitly uses 273.15K and 373.15K rather than 0°C and 100°C.
A temperature of zero Kelvin (absolute zero) makes the ratio undefined for a starting temperature, so the calculator declines to show a result for that input.
Why must temperature be in kelvin, not Celsius or Fahrenheit?
Charles’s law relies on temperature being measured from true zero (absolute zero) — using Celsius or Fahrenheit, whose zero points are arbitrary, would break the direct proportionality the law depends on.
What happens to gas volume as temperature approaches absolute zero?
In the idealized law, volume would shrink toward zero — in reality, gases condense into liquids (and eventually solids) long before reaching absolute zero, so the law only strictly applies to an ideal gas.
Does this work if the gas is being cooled instead of heated?
Yes — enter a final temperature lower than the initial one, and the calculator returns a correspondingly smaller final volume.
