A standard cubic foot (scf) is a unit used both in the natural gas industry to represent an amount of natural gas and in other industries where other gases are used. It is the unit commonly used when following the customary system, a collection of standards set by the National Institute of Standards and Technology. Another unit used for the same purpose is the standard cubic metre (Sm3), customary when using SI units. Definitions A standard cubic foot defines an amount of gas contained in a volume of one cubic foot at standard temperature and pressure. This standard unit of molecular quantity for gases can be used with the ideal gas law to compute the quantity per unit of volume for other pressures and temperatures. In spite of the label "standard", there is a variety of definitions, mainly depending on the type of gas. Since, for a given volume, the quantity is proportional to the pressure and temperature, each definition fixes base values for pressure and temperature. Natural gas Since natural gas is an imprecise mix of various molecular species, chiefly methane but with varying proportions of other gases, a standard cubic foot of natural gas does not represent a precise unit of mass, but a molecular quantity, expressed in moles. For petroleum gases, the standard cubic foot (scf) is defined as one cubic foot of gas at and at normal sea level air pressure. The pressure definition differs between sources, but are all close to normal sea level air pressure. A pressure of . This is the same pressure as the SI system standard pressure. Gives 1.1953 moles per scf. A pressure of . Gives 1.1956 moles per scf. A pressure of . This value is very close to 30 inches of mercury. Gives 1.1981 moles per scf or 0.002641 pound moles per scf. The standard cubic meter of gas (scm) is used in the context of the SI system. It is similarly defined as the quantity of gas contained in a cubic meter at a temperature of and a pressure of . Converting volume units between the standard cubic foot and the standard cubic meter is not exact, as the base temperature and pressure used are different, but for most practical situations the difference can be ignored. Comparing the same volume between the and 101.325 kPa standard cubic meter versus the and standard cubic foot gives an error