Solve PV = nRT for pressure, volume, moles or temperature, with units like atm, kPa, mmHg, L, mL, °C and K converted for you. Switch to the combined gas law (which covers Boyle’s, Charles’s and Gay-Lussac’s laws) to see how a gas changes between two states.
The gas law formulas
Worked example
What volume does 1 mol of gas occupy at 1 atm and 0 °C? Convert T to 273.15 K, then V = nRT/P = 1 × 0.08206 × 273.15 ÷ 1 = 22.41 L, the familiar molar volume at STP. The calculator converts every unit to SI first, so you can mix atm, mL and °C freely.
Always use absolute temperature (kelvin). Using °C directly is the most common mistake in gas law problems. Real gases deviate from ideal behaviour at high pressures and low temperatures.
Frequently asked questions
What is the ideal gas law?
PV = nRT relates pressure, volume, amount (moles) and absolute temperature of an ideal gas, with R the gas constant. Leave one box empty and the calculator solves for it.
Which value of R should I use?
Any, as long as the units match. This calculator works in SI internally (R = 8.314 J/mol·K) and converts your units, so you don’t have to choose.
Why must temperature be in kelvin?
Gas volume and pressure are proportional to absolute temperature. Celsius has an arbitrary zero, so ratios like T₂/T₁ are only correct in kelvin. Pick °C and the calculator converts for you.
When should I use the combined gas law?
When the same sample of gas changes from one set of conditions to another and the amount stays constant. It combines Boyle’s, Charles’s and Gay-Lussac’s laws.
Related tools
Free educational tool by HawkInc. Results are calculated in your browser and rounded for display; check critical work by hand or with a second method.