Ideal Gas Law Calculator (Moles, PV=nRT)
Solve PV = nRT for the number of moles of a gas from its pressure, volume and temperature.
How it works
PV = nRT · n = PV ÷ (R·T) · R = 0.082057 L·atm/(mol·K) · T in kelvin
The ideal gas law ties together the pressure, volume, temperature and amount of a gas through the gas constant R. Rearranged to n = PV ÷ RT, it finds how many moles of gas occupy a given volume at a stated pressure and temperature. This version uses R in L·atm/(mol·K), so keep pressure in atmospheres, volume in litres and temperature in kelvin.
Worked example
At standard conditions — 1 atm, 22.4 L and 273.15 K — n = (1 × 22.4) ÷ (0.082057 × 273.15) ≈ 1.00 mol, the familiar molar volume of an ideal gas at STP.
Sources: Ideal gas law — Wikipedia
Frequently asked questions
Which value of R should I use?
It depends on your units. This tool uses 0.082057 L·atm/(mol·K), which pairs with atmospheres, litres and kelvin. If you work in pascals and cubic metres, use R = 8.314 J/(mol·K) instead.
Why must temperature be in kelvin?
The law uses absolute temperature measured from absolute zero. Celsius values must be converted by adding 273.15 first, or the ratio — and any negative Celsius value — would give a wrong or impossible result.
When does the ideal gas law break down?
At high pressure and low temperature, where molecules are close enough that their size and mutual attractions matter. Real gases then need corrections such as the van der Waals equation.
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Educational estimate. Check the formula, units and significant figures for your exact case.