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Charles's Law describes how the volume of a fixed amount of gas relates to its temperature when pressure stays constant: heat a gas and it expands, cool it and it contracts, in direct proportion to its absolute temperature. This calculator solves for whichever value is missing.
How it works
Enter temperatures in Celsius for convenience — the calculator converts them to Kelvin internally (K = °C + 273.15) since the law requires absolute temperature. Enter any 3 of the 4 values (initial volume, initial temperature, final volume, final temperature) and leave the one you want to solve for blank.
- Enter volume 1 (V₁) — leave blank to solve for this.
- Enter temperature 1 (°C) — leave blank to solve for this.
- Enter volume 2 (V₂) — leave blank to solve for this.
- Enter temperature 2 (°C) — leave blank to solve for this.
- Click Calculate to see your results.
Examples
Heating a gas
A gas at 2 L and 0°C (273.15 K) is heated to 100°C (373.15 K) at constant pressure — its new volume is about 2.73 L, since volume scales directly with absolute temperature.
Who should use it
- Chemistry and physics coursework on gas laws.
- Estimating volume change from heating or cooling a gas at constant pressure.
Industry applications
- Chemistry and physics education
- HVAC and basic thermal-expansion estimation
Advantages
- Simple, exact relationship for constant-pressure gas problems.
- Directly shows why gases expand when heated.
Limitations
- Only valid at constant pressure — use the Combined Gas Law if pressure changes too.
Common mistakes to avoid
- Plugging Celsius values directly into the ratio without converting to Kelvin first — this is the single most common error with this law.
- Assuming pressure is constant when it actually isn't — use the Combined Gas Law if pressure also changes.
Best practices
- Always think in Kelvin when reasoning about this law, even if you enter and read results in Celsius.
- Confirm pressure is genuinely constant between the two states.
Tips
- A quick sanity check: if you're heating the gas, the new volume should always come out larger — if it doesn't, double-check which temperature is which.