Ideal Gas Law Calculator
Solve the ideal gas law for pressure, volume, amount or temperature — PV = nRT — with pressure in kPa, volume in litres and temperature in kelvin or Celsius.
Pressure, volume, moles and temperature — give three, get the fourth.
How the ideal gas law calculator works
The ideal gas law ties together pressure, volume, amount and temperature: PV = nRT, with R = 8.314 J/(mol·K). It holds well for ordinary gases at everyday pressures. Choose the unknown, enter the other three (pressure in kilopascals, volume in litres, temperature in either kelvin or degrees Celsius), and the calculator converts to SI, solves and converts back.
One mole of any gas occupies 22.4 L at 0 °C and 101.325 kPa, and 24.5 L at 25 °C — the numbers chemists memorise.
Formula: P V = n R T (R = 8.314 J/mol·K)
Worked examples
| Inputs | Result | Note |
|---|---|---|
| 1 mol at 0 °C and 101.325 kPa → volume | 22.414 | 22.41 L — the molar volume at STP |
| 1 mol at 25 °C → volume | 24.4654 | 24.47 L |
| 2 mol in 10 L at 300 K → pressure | 498.8678 | 498.9 kPa |
FAQFrequently asked questions
What is R?
The universal gas constant, 8.314 J/(mol·K). In other units it is 0.08206 L·atm/(mol·K) — the calculator works in SI and converts.
When is a gas not ideal?
At high pressure or near its boiling point, where molecules are close enough to interact. Air at room conditions is within 1% of ideal.
Why must temperature be in kelvin?
Because the law is proportional to absolute temperature. 0 °C is 273.15 K, not zero — halving the Celsius figure does not halve the volume.
How many moles are in a litre of air?
At 25 °C and 1 atm, 1 ÷ 24.47 ≈ 0.041 mol — about 1.2 g.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Measurement Institute — Australia's measurement authority
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.