Gas
Gas volume reference conversion
- where
- volume at reference conditions (m³)
- measured volume (m³)
- measured absolute pressure (bar)
- reference absolute pressure (bar, same unit as p)
- reference temperature (°C)
- measured gas temperature (°C)
- reference compressibility factor
- measured compressibility factor
Explain this equation
Converts a gas volume measured at one temperature and pressure to what it would occupy at stated reference conditions. It is used when comparing measured volumes with calorific values or data quoted at standard conditions.
V is the measured volume. p and p_ref are the measured and reference absolute pressures, meaning gauge pressure plus atmosphere. T and T_ref are the gas temperatures in °C. Z and Z_ref are compressibility factors that correct for gas not behaving perfectly; near atmospheric pressure they are close to 1.
It comes from the gas law pV = ZnRT. For the same amount of gas, volume falls as pressure rises and grows as temperature rises. Adding 273.15 converts °C to kelvin, because the law only works on absolute temperature.
Sense check: 1 m³ at 20 mbar gauge and 20 °C becomes about 1.002 m³ at 1.01325 bar and 15 °C. The effects largely cancel at domestic pressures.
Watch out: using gauge pressures gives a badly wrong answer. No water-vapour correction is included.
Enter your values to see the result.
Good to know
Absolute pressures and Kelvin temperatures are essential. Dry/wet gas conditions must be consistent; no water-vapour correction is included.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.