Ideal Gas Law Calculator
Solve PV = nRT for pressure, volume, moles or temperature with the gas constant R = 8.314. Enter any three to find the fourth.
Leave 0 if solving for pressure.
Pressure
101.32 kPa
Volume
22.41 L
Amount of gas
1 mol
Temperature
273.15 K
Ideal gas law: PV = nRT with R = 8.314 J/(mol·K). Enter any three quantities to find the fourth.
Last updated: August 2026
How this calculator is verified
Checked by True Calculator automated test suite on
- Formula verified against a published worked example in the automated test suite
- Edge cases (zero, negative, boundary and unit-mismatch inputs) covered by unit tests
The full verification method is on our how we verify page. Found an error? Tell us and we will re-check it.
When to Use This Calculator
The ideal gas law is the workhorse of Class 11 chemistry and physics in India — NEET and JEE questions regularly ask for the pressure of a gas in a cylinder, the volume of a balloon at altitude, or the moles in an auto-rickshaw tyre at a given temperature. Engineers use the same equation while designing compressed-air systems, gas cylinders and scuba tanks, and it explains why a LPG cylinder feels lighter after heavy use. Whenever three of the four quantities — pressure, volume, moles, temperature — are known and the fourth is needed, this calculator solves PV = nRT in seconds with the standard constant R = 8.314 J/(mol·K).
How to Use This Calculator
- Step 1: Pick which quantity you want to solve for — pressure, volume, moles or temperature.
- Step 2: Enter the three known values in their units (kPa, litres, mol, kelvin).
- Step 3: Leave the quantity you are solving for as 0 or blank.
- Step 4: Read the computed value; all four quantities are shown together for reference.
Worked Example
A chemistry student in an Indian lab wants the pressure of 1 mole of gas at 273.15 K in a 22.414 litre flask. Choose 'Pressure', enter volume 22.414, moles 1 and temperature 273.15. The gas law gives P = nRT ÷ V = 1 × 8.314 × 273.15 ÷ 0.022414, which comes to about 101.32 kPa — the standard atmospheric pressure at STP. Reversing it, with pressure 101.325 kPa and the same moles and temperature, the calculator returns the familiar molar volume of 22.41 litres.
Tips and Common Mistakes
- •Tip 1: Always use kelvin — 0 °C is 273.15 K, and room temperature is about 300 K.
- •Tip 2: The calculator needs three positive known values; the one set to 0 is the one being solved.
- •Tip 3: Use it to check the STP molar volume of 22.41 L — a classic exam result.
- ✗Mistake 1: Entering temperature in °C instead of kelvin, which makes every answer wrong.
- ✗Mistake 2: Leaving more than one field at zero — the law needs exactly three known quantities.
Frequently Asked Questions
What is the ideal gas law?
PV = nRT, where P is pressure, V is volume, n is the amount of gas in moles, R is the gas constant (8.314 J/(mol·K)) and T is temperature in kelvin.
Why is temperature in kelvin?
The ideal gas law is only valid on the absolute temperature scale. 0 °C is 273.15 K — the calculator accepts temperature in kelvin, so enter 273.15 for 0 °C.
How do I find the volume of one mole at STP?
Enter pressure 101.325 kPa, amount 1 mol and temperature 273.15 K, then choose 'Volume'. The answer is 22.41 L, the standard molar volume at STP.
When is the ideal gas law not accurate?
It is an approximation. Real gases deviate at very high pressure or low temperature, for example in LPG cylinders or near condensation, where real-gas equations give better results.
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