CFM vs. SCFM

In the realm of measurement units there are a lot of factors to consider. There are the co-called SI units, and on the other hand, there are the non-SI units. Two highly technical units for gas are SCFM and CFM. Continue to read to learn more about the two.

SCFM is completely known as Standard Cubic Feet / (per) Minute. It shows the gas’ volume flow rate when placed in a controlled environment: Standard temperature, standard pressure and even a standardized relative humidity. This standardization gives way to the measurement of the (mass flow rate) mass of a thing or substance that travels through a certain surface in a specific unit of time. However, it must be made known that the standards can actually vary from place to place. There is still no clear group consensus in determining what the ‘world standard’ really is. For temperature it can vary, like 68°F, 0°C, 15°C or 20°C, among others. For pressure it can be 14.73 psia, whereas others accept 14.696 psia. These variations will become more evident as you travel, let’s say from America to Europe, where you will see that U.S.A.’s temperature standard is 60 to 70° Fahrenheit and in Europe it will be 0°C. Take note, this is not always the case. These values are just the most commonly used. The result is a varying answer of volumetric flow rates. If one uses the temperature 0°C while the other computes the equation using 60°F, their answer will really be different.

The concept of CFM, or Cubic Feet / (per) Minute, is also confusing. Up to this date, there is no one overall definition that describes what a CFM really is. It is the air volume that occurs at an exact temperature or pressure.

In the simplest terms, here’s how you can picture the difference between SCFM and CFM. This is the situation: when you have an air balloon that’s one ft3, and you also happen to be situated in a warm room with a relatively high pressure; when you get out the flow rate will be about 1 CFM. However, what happens is the balloon actually expands as it adapts to the environmental condition outside, which is most likely closer to the standard rate. In this instance, the volumetric flow rate can be perceived as 3 to 4 SCFM. The two measures can be utilized interchangeably, yet it’s better to use SCFM in most types of industries because it can also tell you the values of temperature and pressure.

1. CFM is Cubic Feet per Minute, while SCFM is Standard Cubic Feet per Minute.

2. SCFM is the volumetric flow rate against a standard, whereas there’s no standard for CFM.

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