Volume correction factor (VCF) is a tool chemists often use in their calculations to correct a random volume of gas in their equations to a standard volume. The result of the math is the ratio of the two volumes. Certain calculations depend on using a standard volume, such as determining energy content. The equation for determining VCF uses mostly standard quantities, including the freezing point of water in Kelvin, as well as standard atmospheric pressure.

Add the ambient pressure and the gas meter pressure. For example, assume the ambient pressure is 1 bar and the gas meter pressure reading is 2 bars, giving a result of 3 bars.

Multiply the previous step's result by 273.15 Kelvin, which is the freezing point of water in Kelvins. For example, 3 times 273.15 is 819.45 Kelvin-bars.

Multiply the gas temperature by the standard atmospheric pressure, 1.01325 bars. For example, 400 Kelvin times 1.01325 bars is 405.3 Kelvin-bars.

Multiply the previous step's result by the gas law deviation factor, if given. The gas law deviation factor is a dimensionless measure of the gas's deviation from the ideal gas law due to extreme pressures. Under ideal conditions, its value is one.

Divide the second step's result by the previous step's result to obtain the volume correction factor. For example, 819.45 Kelvin-bars divided by 405.3 Kelvin-bars yields a VCF of 2.022.