Standard Cubic Feet Per Minute

Standard cubic feet per minute (SCFM) is the volumetric flow rate of a gas corrected to "standardized" conditions of temperature and pressure, making it the equivalent of the mass flow rate of the gas. However, great care must be taken, as the "standard" conditions vary between definitions and should therefore always be checked. Worldwide, the "standard" condition for pressure is variously defined as an absolute pressure of 101,325 pascals, 1.0 bar (i.e., 100,000 pascals), 14.73 psia, or 14.696 psia and the "standard" temperature is variously defined as 68 °F, 60 °F, 0 °C, 15 °C, 20 °C, or 25 °C. The relative humidity (e.g., 36% or 0%) is also included in some definitions of standard conditions. There is, in fact, no universally accepted set of standard conditions. (See Standard conditions for temperature and pressure).

The temperature variation has the largest effect. In Europe, the standard temperature is most commonly defined as 0 °C, but not always. In the United States, the standard temperature is most commonly defined as 60 °F or 70 °F, but again, not always. A variation in standard temperature can result in a significant volumetric variation for the same mass flow rate. For example, a mass flow rate of 1,000 kg/h of air at 1 atmosphere of absolute pressure is 455 SCFM when defined at 32 °F (0 °C) but 481 SCFM when defined at 60 °F (16 °C).

In countries using the SI metric system of unit, the term "normal cubic metre" (Nm3) is very often used to denote gas volumes at some normalized or standard condition. Again, as noted above, there is no universally accepted set of normalized or standard conditions.