The Difference Between PSI and CFM Explained

If you’re thinking about buying a new air compressor, two key measurements that you need to be familiar with are PSI and CFM. Understanding what these measurements are, how they relate to one another, and how they affect the performance of your air tools will go a long way towards helping you find the right air compressor for your needs.

Although PSI and CFM are closely related, their difference lies in what they measure. PSI, or Pounds per Square Inch is used to measure force whereas CFM, or Cubic Feet per Minute, is used to measure volume. In simpler terms, PSI represents the pressure of the air that a given compressor can provide while CFM represents the amount of air that can be supplied. Both of these measurements, along with HP (horsepower), duty cycle, and tank size, help gauge an air compressors overall abilities and should be thoroughly considered prior to purchasing a new air compressor.

Throughout the rest of this article, we’ll take a closer look at PSI and CFM so you can determine which air compressor is right for you.

What is PSI?

PSI (Pounds per Square Inch) represents the amount of pressure being applied to a single square inch of space. To help visualize what this looks like, imagine a 200 pound man standing on a single toe in an area roughly the size of a stamp. Because all of his bodyweight is centered in a one square inch area he is delivering 200 PSI. If he were to place his entire foot on the ground, however, he would no longer be delivering 200 PSI because his body weight wouldn’t be centered to a single square inch spot.

How Much PSI do I Need?

The only way to determine how much PSI you need is to first determine what kind of air tools you’ll be using and what their PSI requirements are. Most air tools operate in the range of 70-90 PSI but you should be able to find the specific PSI requirements for your tools in their owners manual.

That being said, most air compressors on the market today are capable of producing up to 150 PSI, which is more than enough to power all the air tools you’d typically be using at home. If, however, your tools require more than 150 PSI, you’ll have to find a more adequate air compressor that can produce the amount of pressure you need.

Respect Your Tool’s PSI Ratings

Another thing to mention is that all air tools have specific PSI ratings that they’re designed to operate at. If you don’t provide them with enough PSI then they may not function properly. If you give them too much you could damage them. Always use your air tools in accordance with their specific PSI requirements.

Remember, just because an air compressor is capable of producing 150 PSI doesn’t mean you have to supply that amount to your tools. Doing so won’t improve their performance. Be sure to regulate the amount of PSI being supplied to your air tools by adjusting your regulator as necessary. Also, be sure to check your gauges periodically just to make sure your operating in the safe zone.

If you’re not sure how to use an air compressor or how to regulate its PSI then be sure to check out my article on using an air compressor for the first time for a complete walkthrough.

What is CFM?

CFM (Cubic Feet per Minute) represents the amount of compressed air being supplied in one minutes time. It has nothing to do with the force or pressure of the air being supplied, but its quantity or volume. If your air compressor has a rating of 5.3 CFM, this means that is capable of producing 5.3 cubic feet of air per minute that its running.

To help put that in perspective, one cubic foot is equivalent to about 7.5 gallons in terms of volume. A cubic foot can also be visualized as a cube that measures 12″x12″x12″.

1 Cubic Foot

Another way of understanding CFM is to view it as the compressors flow rate or output of air. Every air tool needs a specific amount of compressed air in order to operate. Whether or not a given compressor can meet that requirement will be determined by how much air its able to produce.

How Many CFM Do I Need?

Just like PSI, every air tool has a specific CFM rating at which it was designed to operate. If your compressor isn’t rated high enough to match your air tools requirements, then your air tools aren’t going to function properly. With that in mind, its crucial that you select an air compressor that produces enough CFM to run all your air tools efficiently.

To figure out how many CFM you need you’ll first need to see how many CFM your air tools require and then multiply that number by 1.5. For example, lets say the most demanding air tool you plan on using is an air grinder that needs 4 CFM to operate, you’ll want to buy an air compressor with a CFM rating of at least 6.

*4 x 1.5 = 6 CFM

If you plan on running multiple air tools at the same time, you’ll want to add their respective CFM requirements together and multiply that number by 1.5. If, for example, you plan on running an air grinder that needs 4 CFM to operate and a 1/4 air ratchet that needs 4.2 CFM, you’ll need an air compressor capable of producing 12.3 CFM.

*4 + 4.2 x 1.5 = 12.3 CFM

Pay Attention to CFM

When it comes to selecting an air compressor, the CFM rating is a bit more critical than the PSI rating. Because most compressors for home use are rated for 150 – 175 PSI, they’re more than capable of producing enough pressure for most air tools to operate properly. CFM ratings, on the other hand, can vary drastically. That being said, don’t just assume that the compressor you’re thinking about buying will work simply because it produces 150 PSI. If it’s CFM rating isn’t high enough to meet the requirements of your air tools, its simply not going to work for you.

What Size Air Compressor Do I Need?

So, what size air compressor do you need? If you’ve made it this far in the article you probably realize that there’s no blanket answer to this question. What size compressor you need will depend largely upon the tools that you’ll be using and their respective PSI and CFM requirements. That being said, I’ve decided to put together an Air Tool CFM Chart of some common air tools to help give you an idea of what size air compressor you’ll need.

Air Tool CFM Chart

ToolWorking PressureCFM RequirementMin. Compressor Rating
Brad Nailer60-90 PSI11.5 CFM
Framing Nailer90 PSI2.53.7 CFM
Roofing Nailer70-120 PSI2.53.7 CFM
1/4 Ratchet90 PSI4.26.3 CFM
3/8 Ratchet90 PSI4.46.6 CFM
3/8 Air Drill90 PSI6.810.2 CFM
1/2 Impact Wrench90 PSI57.5 CFM
1/4 Angle Die Grinder90 PSI4.56.7 CFM
Air Hammer90 PSI4.46.6 CFM
6″ Palm Sander90 PSI4.56.7 CFM
HVLP Paint Spray Gun30 PSI8 CFM12 CFM
3″ Cut Off Tool90 PSI4.5 CFM6.7
*Please note that the PSI and CFM requirements provided in this table may differ from those of your specific air tools. This table should be used for reference only. Please check the specific air consumption requirements of your air tools prior to purchasing an air compressor.

This table is far from exhaustive but it gives a pretty good idea of the CFM requirements of different air tools and what size air compressor is needed to power them.

If you’d like to learn more about the different operational metrics used to gauge an air compressors overall abilities, check out the following articles:

Or, if you want to know what size air compressor you need for your home garage, check out this article:

Justin

Justin is a full-time blogger with a passion for anything DIY. When he's not hanging out with his wife and son, you can find him putting the finishing touches on yet another home project he's taken on. He's also the creator of AllAboutAirCompressors.com.