What is the gas standard state

Gas "standard state" (also known as "standard conditions," corresponding to the unit for volume Nm³ , and the unit for  flow Nm³/h ) is standardized reference conditions established to standardize gas volume measurement and eliminate the effects of temperature and pressure on gas volume. The gas volume is strongly temperature-pressure-dependent: increasing temperature causes the spacing between gas molecules to increase, leading to expansion, while increasing pressure causes molecules to compress, leading to contraction. Therefore, it is necessary to convert the actual gas volume under the working conditions into a volume under standard conditions through "standard conditions", so as to achieve the comparison, measurement and trade settlement of flow rates in different situations.

The core definition of "standard state": unified temperature and pressure benchmarks.

The essence of standard conditions is to set a "fixed temperature (T。) and pressure (P。) benchmark" for gas volume, and the volume of any gas under this benchmark (i.e. "standard volume", Nm³) is comparable.

However, it should be noted that due to historical habits or differences in application scenarios, different countries/industries have different "standard state". There are two main systems for the standard temperature and pressure regulations. In actual use, specific standards must be clarified to avoid confusion.

Comparison of the two main standard conditions systems

Note: Chinese national standard (GB/T 20727-2006) clearly stipulates that the standard conditions for gas flow measurement are 101.325 kPa and 0°C , which is consistent with the ISO standard system.

The core role of "standard state": solving the "incomparability " of gas volumes.

The "actual volume" of a gas (e.g., working volume, symbolized in m³) varies in real time with the on-site temperature (T) and pressure (P), making direct comparison meaningless. The core value of standard conditions is to unify volumes under different working conditions to those under standard conditions through temperature and pressure  conversion, achieving "fair measurement" and "data comparability."