There are a lot of factors one has to look out for when using the measurement units. There are two types of measurement units, one is the SI units and the other is the non-SI units. SCFM and CFM are the two technical units for measuring gas.
CFM vs SCFM
The difference between CFM and SCFM is that CFM does not have any standard pressure, volume, temperature in which the volume flow of gas is to be calculated whereas SCFM has a standard volume, pressure and temperature in which the volume flow rate of gas is measured.
CFM stands for Cubic Feet per Minute and SCFM stands for Standard Cubic Feet per Minute. Although the standards can vary from place to place, having a standardized and controlled environment to measure the rate of flow of a mass is more efficient and easy then to measure the same rate of flow of a mass in a non-standardized situation.
Many people use these terms interchangeably, but when you want to measure the rate of flow of a gas or any other mass in an industry, it is preferable to use the standard cubic feet per minute measurement instead of the CFM.
Comparison Table Between CFM and SCFM
| Parameters of Comparison | CFM | SCFM |
|---|---|---|
| Full form | The full form of CFM is Cubic Feet per Minute. | The full form of SCFM is Standard Cubic Feet per Minute. |
| Standardization | There is no standard condition at which the CFM values should be calculated. | There is a standard volume, pressure, temperature at which the SCFM values must be calculated. |
| Measurement | CFM is a smaller number than SCFM as it is calculated at higher pressure which makes the air volume small. | SCFM is always a bigger number than the CFM as it is calculated at lower pressure which makes the air volume larger. |
| Calculation | To calculate CFM values, the pressure is maintained under 90psi. | To calculate SCFM values, the air or gas is expanded to a standard condition which is around 14.7psi. |
| Indication | CFM is more relevant to the internal capacity of an air compressor. | SCFM is more indicative of how the gas which is pressurized to a standard value will perform at the end point applications. |
What is CFM?
CFM stands for Cubic Feet per Minute. The term itself is very confusing as it does not have a single definition which applies to all situations. When it comes to mass of a gas, a figure of cubic feet per minute cannot be compared with another figure as gases are compressible.
An example of a constant CFM device is a centrifugal fan. CFM describes the volume of air that occurs at an exact pressure or temperature. In comparison to SCFM, CFM values are always a smaller number as they are calculated at a higher pressure which decreases the volume of gas and makes it smaller.
To measure CFM, the pressure is taken to under 90psi. It is more related to the internal capacity of an air compressor. There is no standard temperature or volume at which it is calculated.
What is SCFM?
SCFM stands for Standard Cubic Feet per Minute. It is the molar flow rate of a gas which is subjected to standardized conditions of fixed pressure and temperature. SCFM is related to the mass flow rate of a gas by a multiplicative constant which only depends on the molecular mass of the gas.
There are many standard conditions for pressure, temperature and even standard relative humidity, so while choosing a standard condition care must be taken. The SCFM values are calculated after expanding the air up to a standard pressure of around 14.7 psi.
As the pressure is low, the volume of gas is bigger and thus SCFM is always a greater number than CFM. Although the standard values can differ from place to place, it is still preferable to use the SCFM measurement unit than the CFM.
Main Differences Between CFM and SCFM
- The full form of CFM is Cubic Feet per Minute whereas the full form of SCFM is Standard Cubic Feet per Minute.
- CFM is always a smaller number than SCFM as it is calculated at higher pressure than the SCFM which makes the air volume smaller.
- There are no standardized units for the calculation of CFM whereas for SCFM values, there are a set of standard pressure, temperature and volume at which they must be calculated.
- CFM values are taken under the pressure of 90psi, whereas to calculate scfm, the air is expanded to a standard condition around 14.7 psia.
- CFM is more relevant to the internal capacity of an air compressor, while SCFM is more indicative of how the gas which is pressurized to a standard value will perform at the end point applications.
Conclusion
For the measurement of the rate of flow of any gas, the most used technical measurement units are the CFM and SCFM. The full form of CFM is Cubic Feet per Minute and the full form of SCFM is Standard Cubic Feet per Minute. The main difference that one needs to know about CFM and SCFM is that SCFM requires a whole controlled and standardized environment for it’s calculation whereas CFM does not have any such standard conditions for it’s calculation.
Because of this, SCFM is a more preferred measurement unit as it has a standard temperature, volume and pressure and thus, gives a precise result. Also, when CFM and SCFM values are compared, it is seen that CFM is always smaller in number. This is due to the fact that CFM is measured at a higher pressure which decreases the volume of gas and makes it smaller.
The CFM values are calculated at a pressure under 90psi whereas the SCFM values are calculated after expanding the gas to a standard value of 14.7 psi. The standardized conditions can vary from place to place and so values of the rate of flow of the same mass may be different in other places
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