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Science — Physics
Ideal Gas Law Calculator
Solve PV = nRT for pressure, volume, moles or temperature — enter the other three.
Answer
—
The variable you asked us to solve for.
| Pressure P | — |
|---|---|
| Volume V | — |
| Moles n | — |
| Temperature T | — |
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Enter your figures above to see the step-by-step working.
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How the Ideal Gas Law Calculator Works
The ideal gas law, PV = nRT, ties together the four things that describe a gas: its pressure, the volume it fills, how much of it there is in moles, and its absolute temperature. R is the gas constant that makes the units agree. Fix any three and the fourth is determined, which is exactly what this calculator does — choose what to solve for and it rearranges the equation for you.
Enter pressure in atmospheres, volume in litres, moles, and temperature in kelvin or degrees Celsius (Celsius is converted to kelvin by adding 273.15, because the law only works on an absolute scale). With R = 0.082057 L·atm per mol·kelvin, one mole of any ideal gas fills 22.4 litres at 0 °C and 1 atm — the classic molar volume.
PV = nRT (R = 0.082057 L·atm mol−1 K−1)
Frequently Asked Questions
Why must temperature be in kelvin?
The gas law is proportional to absolute temperature, where zero means zero molecular motion. Celsius has an arbitrary zero, so using it would give nonsense. Enter Celsius if you like — the tool adds 273.15 to convert before calculating.
What value of R does this use?
R = 0.082057 litre-atmospheres per mole-kelvin, which pairs with pressure in atm and volume in litres. If you work in other units (pascals and cubic metres), R would be 8.314 J/mol·K instead.
How accurate is the ideal gas law?
It is very accurate for real gases at everyday temperatures and modest pressures. It drifts when a gas is near its boiling point or under high pressure, where intermolecular forces and molecular volume start to matter and equations like van der Waals do better.
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