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What is air compressor CFM – Calculate CFM in 3 easy steps

CFM stands for cubic feet per minute. It is the measurement of air volume released by the compressor in a minute.

The effectiveness of the compressor is typically determined by the measure of CFM and the corresponding PSI. It is perhaps the most critical number that concerns the air compressor. It also determines the suitability of the compressor for a particular work. The rate of air delivered usually depends on the pressure valves of the machine.

Air compressor CFM tends to vary depending on environmental variables such as atmospheric pressure, humidity, and temperature. It is also an uncertified definition and is therefore used interchangeably with SCFM or Standard cubic feet per minute.

Associated Terms.

Apart from the commonly used term CFM, there are a couple of terms that are used interchangeably. This can be extremely confusing and bewildering to a first-time buyer or someone outside the industry. The terms associated with CFM are explained below.


Scfm stands for standard cubic feet per minute. It is the CFM calculated at sea level. It measures the exact rate of flow of air under standard conditions and controlled environment. The variables taken into account for standard conditions are 36 % relative humidity and a temperature of 68 degrees Fahrenheit at 14.7 PSI of pressure.

Standard cubic feet per minute is a more scientific way of measuring the exact flow of air since the conditions here are standardized.


It stands for actual cubic feet per minute. It measures the actual compressed air delivery from the inlet to the compressor unit. And because it refers to inlet conditions, it is also used interchangeably with ICFM or inlet cubic feet per minute.

This CFM number takes all the variables of temperature, humidity and altitude. Therefore, it expresses the real output of the compressor unit at the current working conditions.

Under standard conditions of temperature and humidity, actual cubic feet per minute is equal to the standard cubic feet per minute.


It stands for displaced cubic feet per minute. That’s the formula that calculates the cylinder bore, number of RPM at which the motor operates and the stroke into CFM rating. It does not take into account the variables such as atmospheric pressure, humidity, temperature, friction or heat. Therefore, this CFM rating is usually the highest.

While purchasing a new air compressor, do not get carried away by this rating of DCFM. Some brands list the DCFM of the tool and not the SCFM.

DCFM rating is the airflow produced in a perfect environment where there is 100% efficiency. And no compressor is 100% efficient.

Making a comparison of these CFM terms can be overwhelming and confusing to an average buyer. CFM ratings work in conjunction with pressure ratings, i.e. PSI. An accurate indicator of a compressor’s power must be expressed as SCFM at a specific PSI number. This is the best way to know which compressor you need for the desired application.

It is to be noted that the conditions vary from place to place. Conditions such as higher altitudes and colder climates can alter the CFM of a compressor drastically. Therefore, SCFM is the most ideal and correct rating that you should consider.

Note that the increase in CFM will result in decreased PSI and vice-versa.

How much CFM do you need?

Air compressors are used in various applications, from household applications to construction tools, and industrial purposes. All these tools require different CFM ratings to operate, and it is imperative to have a thorough understanding of CFM if you’re planning to buy an air compressor. This will help you choose the right type of air compressor you need for your air tools.

For example, higher CFM ratings are required to operate large tools, whereas smaller ones such as a nail gun work fine with low CFM ratings. High CFM rating means more air and vice versa.

Whether you use an air compressor as part of regular work or use it occasionally, the CFM requirements are usually determined by the power tools you engage in your work.

Air tools typically have the recommended CFM determined by the manufacturer. If you need to use a single high powered tool, then the highest CFM of the air tool will tell you the CFM requirement in an air compressor. However, if you need to use multiple tools simultaneously, the best way is to add all the CFMs of each tool, and you will know which air compressor to use.

To run the multiple machines efficiently, it is recommended to employ an air compressor that has 1.25 to 1.5 more CFM than the total requirements of the tools. This is a great way to prevent the compressor unit from overworking and also extending its life.

Another relatively uncommon feature that can affect the CFM requirements is the presence of air receiver tanks in the unit. A low CFM compressor with air receiver tanks in the design can equal the efficiency of a high CFM compressor.

This is notably featured in reciprocating air compressors that have a 100% duty cycle. This is a significant advantage when you are not ready to invest a compressor with high CFM, which are on the pricier range.

CFM ratings determine which size and type of the compressor best suit your required application. Compressors with high CFM are usually more efficient as well as durable.


In general, user’s manuals that offer information of the CFM are calculated at 90 PSI and few at 40 PSI. If you need to figure out the CFM at different PSI such as 20 or 30 PSI, you can easily do so.

Time needed: 10 minutes.

How to calculate CFM
Note: You need to know the full volume of the tank and start with an empty tank.

  1. Fill the tank (time it)

    And while doing this, make sure you find the difference between starting pressure and ending pressure while doing so.

  2. Multiply the result with the tank’s volume.

    For example a * a= b

  3. Divide the result with the total time required to fill the tank. The resultant number will give you the CFM rating of your compressor.

    For example b/time = your CFM