Ideal Gas Law Calculator
Solve PV = nRT for pressure, volume, amount or temperature, with unit conversion and every step. Also covers Boyle's, Charles's and combined gas laws.
What this calculator does
Pick the unknown, enter the other three quantities in the units you have, and get the answer with the gas constant and unit conversions shown.
When you need it
The ideal gas law links pressure, volume, temperature and amount for any gas. It is used to find molar masses of gases, to size gas containers, and in the gas laws chapter of every general chemistry course.
Formulas
- PV = nRT
- R = 0.08206 L·atm/(mol·K) = 8.314 J/(mol·K)
- Combined gas law: P₁V₁ ÷ T₁ = P₂V₂ ÷ T₂
How to use it
- Choose the gas law and the variable you want to find.
- Enter pressure, volume, amount and temperature, choosing the unit for each.
- Temperature must be absolute; the calculator converts °C to kelvin for you.
- Read the result and the substitution step.
Worked example
What volume does 2.00 mol of an ideal gas occupy at 300 K and 1.50 atm?
- V = nRT ÷ P
- V = (2.00 mol × 0.08206 L·atm/(mol·K) × 300 K) ÷ 1.50 atm
- V = 32.8 L
Answer
The gas occupies 32.8 L.
Common mistakes
- Using °C instead of kelvin in the equation.
- Mixing units, such as kPa for pressure with an R given in L·atm.
- Using the ideal gas law for a gas near condensation or at very high pressure.
Related tools
Frequently asked questions
What is the value of R?
R is 0.08206 L·atm/(mol·K), or 8.314 J/(mol·K). Pick the one that matches your pressure and volume units.
What is the molar volume of a gas at STP?
At 273.15 K and 1 atm, one mole of an ideal gas occupies about 22.4 L.
When does the ideal gas law fail?
At high pressure and low temperature, where gas molecules attract each other and take up real space.