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The Combined Gas Law merges Boyle's Law, Charles's Law, and Gay-Lussac's Law into a single relationship for a fixed amount of gas: pressure times volume divided by temperature stays constant. Use it whenever pressure, volume, AND temperature are all changing at once.
How it works
Enter temperatures in Celsius — they're converted to Kelvin internally for the math. Enter 5 of the 6 values (initial and final pressure, volume, and temperature) and leave the one you want to solve for blank. The calculator applies P₁V₁/T₁ = P₂V₂/T₂.
- Enter pressure 1 (P₁) — leave blank to solve for this.
- Enter volume 1 (V₁) — leave blank to solve for this.
- Enter temperature 1 (°C) — leave blank to solve for this.
- Enter pressure 2 (P₂) — 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
All three variables changing
A gas at 1 atm, 10 L, and 0°C is compressed and heated to 2 atm and 100°C — its new volume works out to about 6.83 L.
Who should use it
- Chemistry and physics coursework on gas laws.
- Estimating how pressure, volume, and temperature interact for a fixed gas sample.
Industry applications
- Chemistry and physics education
- Basic thermodynamics and gas-behavior estimation
Advantages
- One formula covers pressure, volume, and temperature changes together.
- Reduces to Boyle's or Charles's Law automatically if one variable happens to stay constant.
Limitations
- Assumes ideal gas behavior — real gases deviate somewhat at very high pressure or very low temperature.
Common mistakes to avoid
- Entering temperature in Celsius or Fahrenheit directly into the ratio without conversion to Kelvin.
- Missing more than one of the six values — exactly one must be left blank to solve for it.
Best practices
- Keep pressure and volume in consistent units across both states.
- Double check the amount of gas genuinely stays fixed — this law assumes no gas is added or removed.
Tips
- If either pressure or temperature happens to be the same in both states, this formula automatically simplifies to Boyle's or Charles's Law — you don't need a separate calculator for that case.