Ideal Gas Law Calculator (PV = nRT)
Use PV = nRT to find any one of pressure, volume, moles or temperature when the other three are known.
How to use this ideal gas law calculator
- 1Select which variable you want to solve for.
- 2Enter the three known values.
- 3Temperature must be in Kelvin (K = °C + 273.15).
- 4STP defaults (T=273.15 K, P=1 atm, n=1 mol) give V=22.414 L — the molar volume of an ideal gas.
How it's calculated
PV = nRT where R = 0.08206 L·atm/(mol·K). T = PV/nR | P = nRT/V | V = nRT/P | n = PV/RT. STP: 0°C, 1 atm → 22.414 L/mol.
About the Ideal Gas Law Calculator
PV = nRT combines Boyle's Law (P ∝ 1/V at constant T), Charles's Law (V ∝ T at constant P), and Avogadro's Law (V ∝ n at constant T, P) into one elegant equation.
Real gases approach ideal behaviour at low pressure and high temperature — conditions where molecules are far apart and intermolecular forces are negligible. For most lab work at ambient conditions, the ideal gas law is accurate to within 1–2%.
Frequently asked questions
What is R in PV=nRT?
R is the universal gas constant. In these units: R = 0.08206 L·atm/(mol·K). In SI units: R = 8.314 J/(mol·K).
When does the ideal gas law fail?
At very high pressures or low temperatures, real gases deviate — molecules are close enough that intermolecular forces matter. The van der Waals equation corrects for this.
What is STP?
Standard Temperature and Pressure: 0°C (273.15 K) and 1 atm. At STP, 1 mole of any ideal gas occupies 22.414 L.