Ideal Gas Law Calculator
The ideal gas law links the pressure, volume, temperature and amount of a gas. It is a close guide for many gases in everyday conditions. Enter the amount, the temperature and the volume to find the pressure.
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How it works
Pressure equals the amount in moles, times the gas constant, times the absolute temperature, divided by the volume. The gas constant is about 8.314 joules per mole per kelvin, and absolute temperature is the Celsius reading plus 273.15.
The law assumes an ideal gas. At very high pressure, or close to the temperature where a gas turns into a liquid, real gases depart from it.
Worked example
1 moles of gas at 68 °F in a 5 gal container have a pressure of about 18.7 psi.
Questions
Why does the temperature have to be in kelvin?
The formula needs temperature counted from absolute zero, so this page adds 273.15 to the Celsius reading. You do not need to convert it yourself.
How do I find the moles of a gas?
Divide its mass by its molar mass. Air, for example, averages close to 29 grams per mole.
Does this suit a tank or a balloon?
It gives a reasonable estimate for air and many other gases in ordinary conditions. Gases at high pressure need a more detailed equation.
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