Work out cng fill quantity instantly with clear inputs, formula shown and shareable results.
CNG mass follows the real gas law m = pV / (Z R T), with R for methane of 0.5183 kJ/kg.K. Compressibility Z falls to around 0.85 at 200 bar, so ideal-gas arithmetic overstates the fill by 15%. Temperature matters greatly: a hot fill loses mass as the gas cools and pressure settles.
Real gas mass
m = p V / (Z R T), with R = 0.5183 kJ/kg.K for methane
Equivalents
Nm3 = mass / 0.717; GGE = mass / 2.567 kg
CNG is stored at very high pressure. Cylinders must be within their certification period and filling must follow the applicable gas cylinder safety standard.
Compression heats the gas, so the cylinder reaches target pressure at high temperature with less mass inside. As it cools, pressure drops and the tank reads part-full. Temperature-compensated fill controls correct for this.
The mass of CNG with the same energy as one US gallon of gasoline, about 2.567 kg. It allows CNG to be priced comparably to liquid fuels.