🎈 Ideal Gas Law Calculator
Solve PV = nRT for any one of pressure, volume, amount, or temperature. Pick your units for each quantity — the calculator converts °C to kelvin and reconciles atm, kPa, Pa, litres, millilitres, and cubic metres.
🎈 Result
Uses PV = nRT with R = 0.082057 L·atm·mol⁻¹·K⁻¹ (equivalently 8.314 J·mol⁻¹·K⁻¹ in Pa·m³); temperatures in °C are converted to kelvin. Assumes ideal-gas behaviour. For educational use — verify against authoritative sources and follow proper lab safety.
Four variables, one constant
PV = nRT ties the state of a gas together: squeeze the volume and pressure rises, warm it and it expands, add moles and it pushes harder. Because R is fixed, fixing any three variables pins the fourth — which is exactly what this calculator does, in whatever units you prefer.
Need the amount in grams instead of moles? Convert with the Molar Mass Calculator, then bring the moles back here.
❓ Frequently Asked Questions
What is the ideal gas law?
PV = nRT relates the pressure (P), volume (V), amount (n, in moles) and absolute temperature (T) of an ideal gas through the gas constant R. Given any three, the fourth is fixed: P = nRT/V, V = nRT/P, n = PV/RT, and T = PV/nR. It is an excellent approximation for real gases at ordinary temperatures and low-to-moderate pressures.
Which value of R does the calculator use?
It uses R = 0.0820573 L·atm·mol⁻¹·K⁻¹, which pairs with pressure in atmospheres, volume in litres, and temperature in kelvin. This is exactly equivalent to the SI value R = 8.314462618 J·mol⁻¹·K⁻¹ used with pascals and cubic metres — the tool converts your chosen units to a consistent set before solving, so either system gives the same answer.
Why must temperature be in kelvin?
The law is written for absolute temperature, where zero means zero thermal energy. Celsius has an arbitrary zero, so it would give wrong (even negative) results. Enter °C if you like and the calculator adds 273.15 to convert to kelvin automatically; internally every calculation uses kelvin.
What is the molar volume at STP?
One mole of an ideal gas at 273.15 K and 1 atm occupies V = nRT/P = 1 × 0.082057 × 273.15 ÷ 1 ≈ 22.414 litres. This classic result falls straight out of the calculator when you solve for V with n = 1, P = 1 atm and T = 273.15 K, and is a handy sanity check.
When does the ideal gas law break down?
At high pressure or low temperature, real gases deviate because molecules take up space and attract one another; equations of state such as van der Waals correct for this. Treat the ideal result as a close estimate under normal conditions. For educational use — verify against authoritative sources and follow proper lab safety with compressed or hazardous gases.