What is Air Compressor CFM?

So what is air compressor CFM? In simple terms, air compressor CFM is a measure of the air flow rate through an air compressor. It is measured in Cubic Feet per Minute.

When you buy an air compressor, the most important specification is usually the CFM, because the higher the CFM, the more air can be compressed in a given amount of time, which means that you can run your compressor harder without having to wait as long for it to refill. This is especially important if you need to use your compressor frequently; a high-CFM model will be able to work faster, meaning that it will be able to provide more relief quickly.

What does SCFM stand for?

SCFM is for Standard Cubic Feet per Minute. This is the more “scientific” or accurate method of measuring. By excluding variances in air temperature and humidity, SCFM seeks to arrive at a more accurate reading. SCFM is calculated under the following conditions: 14.7 psi (0 psig), 68 degrees Fahrenheit, and 36 percent relative humidity.

Another way of putting is that SCFM is based on ‘ideal’ temperature and air pressure circumstances, while CFM is based on ‘real’ air flow rate.

Colder temperatures, higher altitudes, more powerful tools, and air leaks may all affect a compressor‘s cfm output, thus a “standard” must be established to level the playing field and give an uniform method of measuring CFM output. This is done at a set temperature, height (typically sea level), and with no other factors influencing performance.

In the United States, CFM is the standard unit for measuring airflow rate.

The Relationship Between Pressure (PSI) and Flow (CFM)

To make the pneumatic tool in question work efficiently, air compressor operators must understand the relationship between CFM and PSI (Pound (of force) per Square Inch).

The amount of pressure in a compressed air system has a direct influence on the rate of flow, according to Boyle’s law, which reads as follows:

P1 X V1 = P2 X V2

The pressure level of a gas grows in inverse proportion to the volume of its container (where P1 is the initial pressure, V1 is the starting volume, and P2 and V2 are the final pressure and volume, respectively).

How Does HP Affect CFM Requirement?

HP stands for horsepower, or the amount of work a motor can do. When it comes to assessing whether your compressor will work for you, horsepower is less significant than pressure and flow since newer and more efficient compressors can accomplish more with less horsepower. Doing more with less HP can save you energy and provide you with higher returns during the compressor‘s lifetime.

How Does the Compressor‘s Tank Volume Affect CFM?

The size of the compressor‘s tank influences how long the compressor can create air before the motor kicks in to re-pressurize the tank. The larger the tank volume, the longer a consistent level of air pressure can be provided.

Tanks can vary in size from 1 gallon to 80 gallons, however a single power tool may only need a 5 gallon tank at most.

However, the number of tools that will be using the tank at the same time greatly affects the capacity needed. If you’re going to use three power tools at the same time, each with a 5 CFM At 90 PSI rating, you’ll need a compressor with a minimum of 15 CFM output.

How To Calculate Air Compressor CFM?

In order to calculate the air compressor CFM, you need to know CFM required by the rool, the compressor‘s rated capacity (in pounds), the speed at which the compressor is operating (in revolutions per minute or rpm), and the ambient temperature. Then you can use these numbers to calculate the CFM.

So in steps:

  1. Find the required air flow (CFM) of your specific air tool. This information will be in your tools user guide or manufacturers website.
  2. Obtain the compressor‘s rated capacity (in pounds), speed (in revolutions per minute or rpm), and ambient temperature.
  3. To find the minimum required CFM of the compressor you need multiply your tool’s required CFM by 1.5

So if a tool requires 6.5 CFM, we times that by 1.5 (rather than by 1, to give some headroom), which tells us that we need at least a 9.75 CFM rated compressor.

6.5 CFM x 1.5 = 9.75 CFM

You’ll need to multiply the specific CFM of each tool if you’re going to be running numerous tools. The majority of DIY compressors are only capable of running one tool at a time. On bigger, more commercial compressors, you can effectively operate many tools at the same time.

It’s also worth noting that compressor manufacturers are frequently a little creative with their products’ given CFM ratings, and in the real world, often the compressors are found not perform at the levels specified. I found a great video on this subject by AvE who puts it a little more bluntly!


Use an Air Flow Meter to Calculate Actual CFM 

Using an airflow metre is another simple method to assessing your CFM. This will tell you how much flow and how much pressure is coming out of a fitting. Flow metres may be mounted on specific pieces of equipment or whole systems to provide a real-time measurement of consumption. A receiver tank should be built near the flow metre to smooth out peaks and dips in the data for a more accurate reading. Flow metres for point-of-use and in-line measurements are available in a variety of configurations.

What Factors Affect Air Compressor CFM?

So, we know that the higher the CFM rating, the faster the compressor will work. However, there are other factors that also affect compressor efficiency including the the type of air compressor, the size and shape of the impeller, size of the ductwork, the quality of the air being delivered, and the design of the compressor and the quality of the construction. Additionally, a smaller compressor will move a higher air volume per minute than a larger one, but it will also require more energy to operate.

How To Improve Air Compressor CFM?

There are a number of things that you can do to improve air compressor CFM. You can upgrade the air delivery system by installing larger ductwork, you can increase the impeller size, or you can improve the design of the compressor by adding features like variable speed drive or multi-stage fan motors.

Conclusion: Air compressor CFM is a key metric for measuring the performance of an air compressor. It can be calculated from the input and output parameters of an air compressor. There are several factors that affect air compressor CFM, and you can improve its performance by following some best practices.

What is a Good CFM for an Air Compressor?

A CFM of roughly 5 is required for many pneumatic power tools, however this can vary a lot. A pneumatic stapler may only need 0.4 CFM, but an air frame nailer may need 2.2 CFM.

Continuous-use tools demand a larger volume of air, which means a higher CFM rating. A continually revolving sander may have a CFM demand of 9 (9 CFM @ 90 PSI maybe) as it works continuously without stopping, but a nail gun may have a CFM requirement of 2.7, simply because it only performs its purpose for a split second once every few seconds.

A high cfm rating means that the compressor can move a lot of air at a fast pace, which is important for tasks such as inflating tires or pumping water. So if you need a compressor that can handle a lot of work quickly, look for one with a high CFM rating.

But a more accurate answer for “what is a good cfm?”, is that it depends on several factors:

The Number of Air Tools Being Used

Air compressors are used by many different types of industries. In most cases, however, there isn’t much difference in the volume of air required to operate any given tool. A 2″ air grinder may require 30 cfm while a 1″ impact wrench may require 50 cfm. However, when using multiple tools at once, the total amount of air required to run them increases. To ensure that your team can use multiple tools without having to purchase a larger air compressor, make sure you factor in the additional cfm needed to operate multiple tools. Pneumatic tools‘ cfm ratings are already multiplied by 100%. You do not need to calculate duty cycles for each individual device. However, if you are using multiple tools simultaneously, you should multiply the total cfm rating by the number of tools. This will ensure that you get enough air flow to operate all of your tools continuously.

The Type of Tools Being Used

Consider the cfm needs of the air tool or tools you’re using. This information should be included in the tool handbook according to the manufacturer’s instructions. If you’re just utilising one air tool, the minimum cfm rating on your air compressor should be the highest cfm designated for that tool.

When calculating the cfm needs for your air compressor, it’s critical to consider the duty cycle. The duty cycle in this example refers to the amount of time an air compressor can operate before it has to stop to catch up or cool down. A 25 percent duty cycle is used to get the average cfm rating for air tools. As a result, it’s common to suggest that the cfm rating of your compressor be 1.5 times that of your air tool. This setting will keep your air compressor from working too hard.

Consider your compressor‘s cfm requirements on a 100 percent duty cycle if your team has to utilise tools for long periods of time. Additional computations may be required, so it’s critical to think about what tools you’re using and how you’re using them.

Intermittent or Continuous Use?

When evaluating your air compressor‘s cfm requirements, think about how you’ll be using the tool. Do you like to work in short bursts with brief intervals, or do you need to use your equipment for extended amounts of time? Is there enough time for the air compressor to catch up and cool down between uses?

By asking yourself these or similar questions, you can guarantee that you are using your tools for their intended purpose. If your application necessitates the use of air tools for a lengthy period of time, you must calculate the cfm needs of your air compressor using a 100 percent duty cycle. General air tools used for occasional bursts, on the other hand, may be able to get by with a less powerful but more cost-effective compressor.

Our article What Size Air Compressor Do I Need gives the usual CFM requirements (as well as PSI, HP and Tank Size) of all of the most commonly used pneumatic tools, so have a read of that if you’re looking for the CFM for a particular tool.


So there you have it – CFM is both complex and very simple, all at once! Hopefully though you now know how to work out the CFM of the air compressor you need. If you have any more questions, just ask in the comments below.

Jeff Stelling

Jeff Stelling is an air compressor obsessive who has been working with compressors for over 25 years, since he was an apprentice engineer in the mid 90’s. He designed Aircompressorcompare.com to offer technical guidance and buying advice for compressors.

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