Ideal Gas Law Calculator

Written byOleh Soloninupdated 5 October 2026

Solve for

Pressure, kPa

Volume, l

Amount of substance, mol

Temperature, °C

Result

Result22.414
What was calculatedVolume, l
Molar volume, l/mol22.414
Temperature, K273.15
Pressure, atm1
What matters
The equation is exact for an ideal gas; real gases deviate at high pressure and near condensation.

A mole takes 22.4 litres — but not always

Solves the ideal gas law PV = nRT for pressure, volume, amount of substance or temperature, and gives the molar volume at those conditions.

PV = nRT ties four quantities together through the gas constant, 8.314 joules per mole per kelvin. Know any three and the fourth follows uniquely.

The famous 22.4 litres per mole is not a constant but a special case: the volume of one mole at zero degrees and 101.325 kilopascals. At twenty degrees the same mole takes 24 litres, and the textbook figure stops working.

How to use

Choose what to solve for: volume, pressure, temperature or amount of substance.
Enter the other three; temperature goes in degrees Celsius.
Read the answer, the molar volume and the pressure converted to atmospheres.

Molar volume and standard conditions

At 0 °C and 101.325 kPa one mole of an ideal gas occupies 22.414 litres — the figure every chemistry course asks you to memorise. It is not a constant of nature but a consequence of pV = nRT at those particular conditions.

The equation accepts temperature only in kelvin, which is the commonest source of nonsense results: 0 °C is 273.15 K, not zero. Feed it degrees Celsius and every other correct number will still produce a wrong answer.

Worked out with this calculator for an ideal gas.
Conditions	Temperature	Pressure	Volume of one mole
Standard	0 °C	101.325 kPa	22.414 l
Room	25 °C	101.325 kPa	24.465 l
Cold	−20 °C	101.325 kPa	20.773 l

What this calculator shows

Any of the four quantities in the equation
The molar volume at the conditions given
Pressure in atmospheres and temperature in kelvin

What to keep in mind

Temperature is always converted to kelvin: the equation only works on an absolute scale.
The ideal gas model ignores molecular volume and attraction, so deviation grows at high pressure and near condensation.

FAQs

What is the gas constant?

8.314462618 joules per mole per kelvin. With pressure in kilopascals and volume in litres it is used in exactly that form.

Why does one mole of gas take 22.4 litres?

That is the volume at 0 °C and 101.325 kPa. At 25 °C and the same 101.325 kPa the same mole takes 24.47 litres.

Why convert temperature to kelvin?

Because the equation is linear in absolute temperature. Zero on the Celsius scale does not mean the absence of thermal motion, and the formula would break.

How accurate is it for real gases?

For dilute gases at ordinary conditions, within a percent. Near condensation and at high pressure, real gases deviate noticeably.

Why does a mole of gas occupy 22.4 litres?

It follows from pV = nRT at 0 °C and 101.325 kPa. At a room temperature of 25 °C the same mole takes 24.465 litres.

Which temperature unit does the equation need?

Kelvin only: add 273.15 to degrees Celsius. Substituting zero instead of 273.15 K is the classic error here.

How far off is a real gas?

The error depends on the gas, the pressure and the temperature; the compressibility factor Z for that gas tells you how far off the ideal model is. Deviations grow under high pressure and near the condensation point, where molecules stop behaving independently.

Worked example

Standard conditions

Input: 1 mole, 101.325 kPa, 0 °C

Output: 22.414 litres

Note: The textbook 22.4 litres. Raise the temperature to a room-like twenty degrees and the volume climbs to 24.06 litres — almost eight percent more.

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Result

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