Combined Gas Law Calculator
When a fixed amount of gas changes pressure and temperature, its volume changes too. Enter the starting conditions, then the new pressure and temperature, and this page finds the new volume.
- Free
- Works offline after your first visit
- Saves on this device
- No sign-up
- Updated
How it works
For a fixed amount of gas, pressure times volume, divided by absolute temperature, stays the same. The new volume is the starting volume times the starting pressure and the new temperature, divided by the starting temperature and the new pressure.
Temperatures can be entered in Fahrenheit or Celsius. They are converted to kelvin first, because the law needs absolute temperature.
Worked example
A gas starting at 15 psi, in 1 gal, at 68 °F ends up at 30 psi and 140 °F, with a new volume of 0.57 gal.
Questions
Why does a warmer gas take up more room?
At the same pressure, warmer gas spreads out, because its molecules move faster and push harder on their container.
Does the amount of gas have to stay the same?
Yes. The law applies to a fixed amount of gas. If gas is added or lost, a different calculation is needed.
Which temperature scale should I use?
Either one. Pick Fahrenheit or Celsius, and the calculator converts to kelvin before it does the math.
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