Thermodynamics
Ideal Gas Law Calculator
Solve PV = nRT for pressure, volume, moles or temperature. Full unit conversion — pascals, atm, bar, litres, kelvin, celsius and fahrenheit.
Solve for
PV = nRT
R = 8.314 J/(mol·K)
Standard conditions
Fill in the three known values above.
Gas law equations
Ideal Gas Law
PV = nRT
Solve for P
P = nRT / V
Solve for V
V = nRT / P
Solve for n
n = PV / RT
Solve for T
T = PV / nR
Combined gas law
P₁V₁/T₁ = P₂V₂/T₂
The ideal gas law
The ideal gas law PV = nRT combines Boyle's law (P ∝ 1/V), Charles's law (V ∝ T) and Avogadro's law (V ∝ n) into a single equation. It assumes gas molecules have no volume and no intermolecular forces — a good approximation for real gases at low pressures and high temperatures.
The universal gas constant R = 8.314 J/(mol·K) links the macroscopic (pressure, volume, temperature) to the microscopic (number of molecules via moles). At STP (0°C, 1 atm), one mole of any ideal gas occupies 22.4 litres — the molar volume.
When does the ideal gas law break down?↓
At high pressures (molecules are forced together — their volume matters) and low temperatures (intermolecular forces become significant). The van der Waals equation adds correction terms for both effects.
What is the difference between STP and SATP?↓
STP (Standard Temperature and Pressure) is 0°C and 1 atm. SATP (Standard Ambient) is 25°C and 1 bar. IUPAC now defines standard pressure as 1 bar (100,000 Pa), not 1 atm (101,325 Pa). Many textbooks still use the old STP.