About Charles' Law
Charles' Law describes how the volume of a gas changes with temperature when pressure and the amount of gas are held constant. First observed by French physicist Jacques Charles in the 1780s and published by Joseph Louis Gay-Lussac in 1802, it states that volume and absolute temperature are directly proportional: V₁/T₁ = V₂/T₂. This calculator uses your initial volume and temperature, plus a target final temperature, to find the resulting final volume.
Understanding the formula
Charles' Law falls out of the ideal gas law, PV = nRT. If pressure (P) and the number of moles (n) do not change, then V/T = nR/P is a constant, so V₁/T₁ must equal V₂/T₂. Rearranging for the unknown gives the final volume directly: V₂ = V₁ × (T₂ / T₁). Because the ratio only means something physical when temperature is measured from absolute zero, every temperature is converted to Kelvin before the calculation runs (K = °C + 273.15, or K = (°F − 32) × 5/9 + 273.15).
Working with temperature units
Enter your initial and final temperatures in Kelvin, Celsius, or Fahrenheit — the calculator converts whichever you pick into Kelvin internally, since Celsius and Fahrenheit both have zero points that are not physically meaningful for a gas's volume. Double-check that a "below zero" entry is still a valid physical state: 0 K (-273.15°C, -459.67°F) is absolute zero, and no real or ideal gas can exist below it, so the calculator rejects any temperature that converts to 0 K or less.
Knowing the limits
Charles' Law assumes an ideal gas at constant pressure and a fixed amount of gas — it does not apply if the gas is compressed, released, or allowed to escape, or if pressure changes during the process (use the combined gas law, P₁V₁/T₁ = P₂V₂/T₂, instead). It is a good approximation for common gases like air, oxygen, or nitrogen at everyday temperatures and pressures — think of a balloon shrinking in cold air or a bicycle tire's pressure rising as it warms in the sun. Near a gas's condensation point or at very high pressure, real-gas effects make the ideal relationship less accurate.