Ideal Gas Law Calculator
Solve the ideal gas law PV = nRT for pressure, volume, moles or temperature using R = 0.082057 L·atm/mol·K.
How it works
PV = nRT · R = 0.082057 L·atm/(mol·K) · P = nRT/V · V = nRT/P · n = PV/RT · T = PV/nR
The ideal gas law ties together the pressure, volume, amount and temperature of a gas that behaves ideally. R is the universal gas constant; in these units it is 0.082057 L·atm per mole per kelvin. Choose which quantity is unknown and the calculator rearranges PV = nRT to solve for it. Temperature must always be in kelvin.
Worked example
One mole of gas at 273.15 K in 22.4 L gives P = (1 × 0.082057 × 273.15) ÷ 22.4 ≈ 1.00 atm — the familiar molar volume at standard conditions.
Frequently asked questions
Why must temperature be in kelvin?
The gas law is built on absolute temperature. Using Celsius would make the equation fail at and below 0°C, so always convert to kelvin by adding 273.15.
What does "ideal" gas mean?
An ideal gas has point-like molecules with no attraction between them. Real gases follow the law closely at ordinary pressures and temperatures but deviate when very cold or highly compressed.
Which value of R should I use?
It depends on your units. This calculator uses 0.082057 L·atm/(mol·K) because pressure is in atmospheres and volume in litres. With pascals and cubic metres you would use 8.314 J/(mol·K).
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Educational estimate. Check the formula and units for your exact case.