What is CFM in Compressed Air?

CFM is the abbreviation for cubic feet per minute (cu ft/min). It is a measurement of how fast air flows into or out of a space. In compressed air, this means it is a measure of the flow or output rate that air is coming out of your compressor.

What is the Relationship Between CFM and PSI?

CFM is the “Flow” or the compressor’s ability to continue performing a certain task over time. It expresses the amount of flow needed and depends on the length of time required to complete the task. With insufficient flow, the compressor will require breaks to rebuild pressure in the compressor’s reserve tank.

PSI (Pounds per Square Inch) is the “Pressure”. It expresses the compressor’s ability to perform a specified amount of work at any given point in time. The compressor must provide the right amount of pressure, or force, needed to complete the process.

In compressed air terms, pressure delivers the force, yet horsepower delivers the flow. Too little pressure means the job won’t get done. Too much pressure can damage the equipment and cause unexpected malfunctions.

Use our air compressor CFM calculator below to help you to quickly and easily calculate your CFM!

Between CFM & PSI, these two measurements essentially define whether a compressor can meet the demand of your equipment. Each piece of production equipment will have a CFM (airflow) requirement. When calculating how much your air compressor’s output rate needs to be, you not only need to consider the requirements of each of your tools, but also how often/how long they will run for.Another fact to consider is how much of your equipment will be running at the same time?

Download a copy of our Air Consumption Calculator for a listing of the air demand of most air driven tools and a handy calculator to figure out what your operation needs, then use the air flow rate calculator.

Read our blog post about Properly Sizing a System to learn more.

Free Online Air Compressor CFM Calculator

Utilizing the Tank Pump-Up Time method, let’s test the efficiency & calculate the CFM of your compressed air system

How Do You Calculate CFM for an Air Compressor?

When customers call us trying to learn about the physics behind compressed air and wanting to understand what is best for them, they ask “how to measure compressed air flow rate?” It may seem complex, but it really is quite easy to do yourself (though our calculator makes it much easier!).

The air compressor cfm psi calculator formula is: CFM = Tank Volume in Cubic Feet x Standard Pressure (ATM) during a cycle x Cranks per Minute

Example: 15 HP Compressor with a 132 Gallon Tank rated for 125 PSI and 54.9 CFM. Let’s work backwards with our formula and see what we get.

  • Convert the capacity of the tank to cubic feet. 1 Cu. Ft. = 7.48 gallons. 132/7.48 = ~17.65 Cu.Ft.
  • Start the compressor and measure the time of the load and unload cycles on the tank gauge.
  • Using a stopwatch (there is one on your smartphone), time how long it takes from when the compressor starts running to the time it stops running. Also watch the tank gauge during this time and record the PSI, both when the compressor starts and stops running. If you are starting up a compressor that has been off, let the tank fill completely once before starting your timing and recording of results.
  • If the compressor loads at 80 PSI and unloads at 120 PSI, this equals a 40 PSI difference (also known as differential pressure).
    • Next, convert to standard pressure (ATM). 1 ATM = 14.7 PSI, 40/14.7 = 2.72
    • Tank Pump-up Time = 1 min 8.4 seconds (1.14 minutes)
    • The three primary factors are:
      • Tank Volume – 17.65 Cu.Ft.
      • Standard Pressure During Cycle (ATM) – 2.72 PSI
      • Cranks per Minute – 1.14 minutes.
    • CFM = Tank Volume in Cubic Feet x Standard Pressure (ATM) During a Cycle x Cranks per Minute
    • 17.65 x 2.72 x 1.14 = 54.7 CFM which is fairly close to our OEMs rating of 54.9. The 0.2 difference is most likely because of the rounding that we did.

The easier way to do all this is simply use our air compressor CFM calculation formula above and it will do all the work for you.

Using a Flow Meter to Calculate CFM (Airflow)

Another easy way to calculate your CFM is by using an airflow meter. This will give you the amount of flow and the pressure that is coming out of a fitting. Flow meters can be installed on individual pieces of equipment or complete systems to provide an instant reading of actual usage. For a more accurate reading, a receiver tank should be installed near the flow meter to even out peaks and valleys in the data. There are different types of flow meters that can be used for point-of-use measuring, and in-line measuring. VIP Instruments has a vast array of different flow meters. If you don’t know which one to choose, give us a call and we will help to walk you through what your system may need.

Contact us at (800)-371-8380 and our air expert will answer all your questions about CFM calculation.