Gas Law Calculator
The ideal gas law ties pressure, volume, temperature and amount of gas together in one equation — this specifically solves for pressure, useful whenever the other three variables are known but pressure needs to be found or verified.
Inputs
Result
1.0917 atm
How it works
PV = nRT
How the gas law calculator works
PV = nRT, rearranged to solve for pressure: P = nRT ÷ V.
R (the ideal gas constant) is used here as 0.082057 L·atm/(mol·K), giving pressure directly in atmospheres when temperature is in Kelvin and volume is in litres.
Worked example: 1 mole of gas at 298 K in a 22.4 L container
- P = (1 × 0.082057 × 298) ÷ 22.4.
- = 24.453 ÷ 22.4 ≈ 1.092 atm.
- This is close to but not exactly 1 atm, since standard conditions for exactly 1 atm (1 mole occupying 22.4 L) technically assume 273.15 K, not 298 K — the slightly higher temperature here raises the pressure somewhat above exactly 1 atm at the same volume.
Common mistakes to avoid
Entering temperature in Celsius instead of Kelvin
The ideal gas law requires absolute temperature (Kelvin) specifically, since it's derived from molecular kinetic energy relationships that only make physical sense on an absolute scale — using Celsius directly (which can be negative or zero) produces a nonsensical or wildly incorrect result.
Assuming the ideal gas law is exactly accurate for all real gases in all conditions
The ideal gas law is an approximation that works very well for many gases under normal conditions, but becomes less accurate at very high pressure or very low temperature, where real gas molecules' own volume and intermolecular attractions start to matter more than the ideal model accounts for.
Frequently asked questions
Why must temperature be in Kelvin for this calculation?
The gas law's derivation relates directly to the average kinetic energy of gas molecules, which is proportional to absolute temperature — Kelvin starts at true zero (no molecular motion), making it the only temperature scale where this direct proportionality holds cleanly.
What does R (the gas constant) actually represent?
It's a fixed proportionality constant that makes the units in the ideal gas law work out consistently — its specific numerical value depends on which units are chosen for pressure, volume and temperature, which is why different textbooks sometimes quote R with different numbers.
Why doesn't this calculator ask for the gas's identity (like whether it's oxygen or nitrogen)?
The ideal gas law treats all gases as behaving identically under the same conditions, regardless of their specific molecular identity — this is a simplifying assumption that holds reasonably well for many real gases under everyday conditions.
How is this related to the other three gas law variables (volume, temperature, moles)?
This specific tool solves for pressure given the other three — rearranging the same PV = nRT relationship differently would let it solve for volume, temperature, or moles instead, given whichever three variables are already known.
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