Thermodynamics
Ideal Gas Law Calculator
Solve PV = nRT for any variable. Supports atm, kPa, bar, Celsius, Fahrenheit and Kelvin.
Result
Step-by-Step Solution
What is the Ideal Gas Law?
The ideal gas law is a fundamental equation in thermodynamics that describes the behaviour of an ideal gas — a theoretical gas in which the molecules have no size and no intermolecular forces. Despite being a simplification, it accurately models the behaviour of most real gases under typical conditions of temperature and pressure.
PV = nRT
P = pressure (Pa) | V = volume (m³) | n = moles | R = 8.314 J/mol·K | T = temperature (K)
Variables Explained
| Symbol | Name | SI Unit | Description |
|---|---|---|---|
| P | Pressure | Pa | Force per unit area exerted by gas molecules on walls |
| V | Volume | m³ | Space occupied by the gas |
| n | Moles | mol | Amount of gas (1 mol = 6.022×10²³ molecules) |
| R | Gas Constant | J/(mol·K) | Universal constant: 8.314 J/mol·K |
| T | Temperature | K | Absolute temperature — must always be in Kelvin |
💡 At STP (Standard Temperature and Pressure: 0°C, 1 atm), one mole of any ideal gas occupies exactly 22.4 litres. This is the molar volume of an ideal gas.
Frequently Asked Questions
What is the gas constant R?
R = 8.314 J/(mol·K) is the universal gas constant. It can also be expressed as 0.08206 L·atm/(mol·K) when using litres and atmospheres. It appears in many thermodynamics equations and connects macroscopic gas properties to the microscopic.
When does the ideal gas law fail?
The ideal gas law breaks down at very high pressures (molecules are too close together for the no-volume assumption to hold) and very low temperatures (near condensation point, where intermolecular attractions matter). The van der Waals equation corrects for these.
How do I convert Celsius to Kelvin?
K = °C + 273.15. Always convert to Kelvin before using the ideal gas law — using Celsius will give wrong answers because the law requires absolute temperature. 0 K = −273.15°C (absolute zero).