Charles's Law Calculator

How it is calculated

Charles's law says that for a fixed amount of gas at constant pressure, volume is proportional to absolute temperature: V₁ / T₁ = V₂ / T₂. The tool solves for the final volume, V₂ = V₁ × T₂ / T₁. V₁ is the starting volume in any volume unit (the answer uses the same unit), and T₁ and T₂ are the starting and final temperatures in kelvin. All three values must be above zero. To convert, K = °C + 273.15, so 27 °C is 300.15 K. Never use Celsius or Fahrenheit directly: the proportion only works from absolute zero. The result is rounded to four decimals. It assumes an ideal gas, a sealed amount of gas, and a pressure that stays the same.

Common mistakes

• Entering temperatures in degrees Celsius. Going from 20 °C to 40 °C is not a doubling; in kelvin it is 293.15 K to 313.15 K, only about a 7% rise.
• Applying the law when pressure changes or gas is added or leaks out; both break the constant pressure and fixed amount assumption.
• Swapping T₁ and T₂, which inverts the ratio and gives a shrinking volume for a heated gas.
• Using it near the point where the gas condenses, where real gases no longer behave like an ideal one.