PSI, CFM, and HP: understanding air compressor measurements

If you’ve been in the air compressor industry for any length of time, you’re likely familiar with the acronyms PSI (pressure), CFM (flow), and HP (power). These principles are essential in determining which size air compressor will fit your application – in fact, PSI, CFM, and HP are some of the most important elements to consider when selecting the best air compressor for your needs.

PSI vs. CFM vs. HP

PSI, CFM, and HP are the three main ratings that showcase exactly what a compressor can do.

• PSI, or pounds per square inch, measures the amount of pressure placed on a square inch of space. In compressor terms, PSI is the amount of force that an air compressor can deliver.
• CFM is cubic feet per minute, which indicates the compressor’s flow rate - or the amount of air that a compressor can produce at a given pressure level. Typically, compressors that have higher CFM ratings are able to provide more air, which makes them ideal for larger applications.
• HP is horsepower, or the amount of work that a motor can perform. HP is not as important as pressure and flow in determining if your compressor will work for you, as newer & more efficient compressors can do more with less HP! Doing more with less HP will save you energy, as well as will give you larger returns throughout the life of the compressor.

What is the difference between PSI and CFM?

While PSI and CFM are both critical air compressor measurements, they describe two completely different characteristics of a compressor's performance, and understanding the difference between the two is key to selecting the right compressor for your needs. 

PSI tells you how hard the air is being pushed. It's a measure of pressure, specifically, the amount of force being delivered per square inch. A higher PSI means the compressor is capable of delivering air at greater pressure, which is important for applications that require a strong, forceful output. 

CFM, on the other hand, tells you how much air is being delivered. It's a measure of flow, the volume of air a compressor can produce per minute at a given pressure level. A higher CFM means the compressor can supply a greater volume of air, which is essential for applications that require a continuous or high-volume air supply. 

Here's a simple way to think about the difference: PSI is the strength of the air, and CFM is the quantity of the air. Both matter, but in different ways depending on your application. A tool or process that requires high pressure but low volume will prioritize PSI, while one that needs a steady, large supply of air will prioritize CFM. Many applications require a careful balance of both. 

It's also important to note that PSI and CFM have an inverse relationship in a compressor system. As pressure (PSI) increases, the available flow (CFM) typically decreases, and vice versa. This is why compressor ratings are always specified together, for example, "10 CFM at 100 PSI", because quoting one without the other doesn't give you the full picture of what the compressor can actually deliver. 

Things to Consider

No matter your application, it’s critical to understand the PSI, CFM, and HP that your application requires. This will ensure that your application receives sufficient air flow (CFM) at the correct pressure (PSI) – and that the air compressor is providing your pressure and flow as efficiently as possible.

Atlas Copco is always available to assist you in your compressor selection. Our experts will guide you in your selection based on your application’s specific needs and rating requirements. Reach out to us today!

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