This ideal gas law calculator solves the equation PV equals nRT for whichever quantity you do not know: the pressure, the volume, the number of moles or the temperature. The ideal gas law ties together the four things that describe a sample of gas, with R the universal gas constant holding the relationship together, and it is one of the cornerstones of chemistry and physics. It captures the intuitive behaviour of gases: squeeze the volume and the pressure rises, heat the gas and it expands or pushes harder, add more gas and the pressure climbs. You choose what to solve for, enter the other three values, and the calculator returns the answer. This tool uses a tidy set of units, pressure in kilopascals, volume in litres, amount in moles and temperature in kelvin, with R taken as 8.314, because in these units a kilopascal times a litre equals a joule and everything stays consistent. The one thing to watch is temperature: the law needs absolute temperature in kelvin, so convert from Celsius by adding 273.15, which makes 25 degrees Celsius 298.15 kelvin. Real gases follow this closely at ordinary temperatures and pressures, drifting only at very high pressure or very low temperature. Enter your three known values to see the fourth straight away.
R = 8.314. Pressure in kPa, volume in L, temperature in K (Celsius plus 273.15). Estimate only.
The calculator rearranges PV equals nRT for the unknown. Pressure is nRT over V, volume is nRT over P, the number of moles is PV over RT, and temperature is PV over nR, all with R equal to 8.314 in the chosen units. The quantity you are solving for is hidden so you enter only the three you know.
One mole of gas at 273.15 kelvin in 22.711 litres has a pressure of 1 times 8.314 times 273.15 over 22.711, which is about 100 kilopascals. This is the molar volume of an ideal gas at standard temperature and pressure.
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