When shopping for an air compressor, or trying to determine what tools you can use with your compressor, you’ll need to know the terminology. And one of the most important factors when dealing with an air compressor is CFM (CFM stands for Cubic Feet per Minute). Read on to learn all about CFM and what it means for getting things done with a compressor.
Table of Contents
- Cubic Feet Per Minute Explained
- What’s the Difference Between CFM and PSI?
- CFM vs SCFM
- What is a Good CFM Rating for an Air Compressor?
- Air Tools and Their CFM
- Can You Increase CFM on an Air Compressor?
Cubic Feet Per Minute Explained
Cubic Feet per Minute (CFM) is a measurement describing how much air pressure a compressor can produce at a given pressure. This is often called the compressor’s flow rate, and it determines what kind of air tools you can use with the compressor. The higher the CFM of a compressor, the more it is capable of.
Also, the higher the CFM measures, the larger the tank size. This is because continuous use tools generally require a higher rating. When operating a high CFM tool on a compressor with a small tank, the compressor will need to cycle on more often, which could mean more downtime using that tool.
But this doesn’t mean that you should run out and buy a compressor with the highest CFM you can find. Depending on what you’ll be using the compressor for, you may not need a compressor with a high rating. This is important because, generally, a higher CFM means a more expensive compressor.
Luckily, we’ll explain everything you need to know about ratings, why to measure airflow, and even giving examples of air tools and their ratings. But before we go any further, it’s important that we discuss two other factors that relate to CFM. These are PSI and SCFM.
What’s the Difference Between CFM and PSI?
PSI, which stands for Pounds per Square Inch, measures pressure. CFM, on the other hand, measures volume. Both are important when considering air compressor factors. Home-use compressors come with a max PSI rating, usually between 150 and 175 PSI. They also come with ratings that tell you how many cubic feet per minute of air the compressor can deliver at a certain PSI.
For example, a small, home-use compressor might have a rating of 2.4 CFM @ 90 PSI. This means it can deliver 2.4 cubic feet per minute at a pressure of 90 pounds per square inch. The CFM is the volume the compressor can deliver, and the PSI is the pressure.
Is CFM More Important Than PSI?
Both CFM and PSI are equally important factors when it comes to air compressors. The two measurements combine to tell you how much pressure or force the compressor is capable of generating (PSI) and the volume it can deliver (CFM).
These two measurements are directly related to each other, as a change in PSI will result in a change in potential CFM. The higher the pounds per square inch in the compressor tank, the higher the potential air flows at a rate in cubic feet per minute.
This is why smaller compressors are only capable of a CFM flow rate somewhere between 0.5 and 5 at 70 to 90 PSI, whereas larger industrial compressors can deliver a flow rate in the hundreds at a corresponding pressure in pounds per square inch.
CFM vs SCFM
Now that we’ve covered what CFM stands for and what PSI means, let’s turn to another unit of measurement you’ll come across in the air compressor world: SCFM. This stands for Standard Cubic Feet per Minute, and is different from CFM.
SCFM is the measure of how many cubic feet per minute a compressor can deliver under ideal conditions. Things like humidity, pressure, and temperature all factor air compression and delivery.
This means that one compressor may be able to deliver a different CFM in a place that’s at sea level, with an ambient temperature in the 70s, and a higher humidity rating than in a place that’s in the mountains with temperatures in the 30s and a low humidity rating.
As such, SCFM is designed to tell you what the compressor can do under ideal conditions, which are: 14.7 psia (0 psig), 68 degrees Fahrenheit, and 36 percent relative humidity.
CFM measurements, on the other hand, are less precise and allow for a margin of error. To accurately measure your CFM, you’d need to know the pressure, temperature, and relative humidity in the area in which you’re using the compressor.
Generally, SCFM is used to describe the air flow from the compressed air at the point of use — at the air tool. CFM is generally used to describe the flow rate of a compressor. It’s also worth noting that CFM is always smaller than SCFM because CFM is measured at a higher pressure, which reduces the air volume.
What is a Good CFM Rating for an Air Compressor?
A “good” rating on an air compressor is wholly dependent on what you plan on using the compressor for. Most portable compressors for home use have a rating between 0.5 and 5. For most people, this is fine.
When CFM measures 5 @ 90 PSI can allow you to operate some basic smaller air tools as well as working well for filling up tires and inflating sports equipment.
But since there’s such a wide range of smaller air compressors out there, you’ll want to determine how much CFM you’ll need by doing a bit of research on the air tools you’ll be using. Once you know the highest CFM requirement for the air tools you’ll be using, you can then determine which compressor will be best for your needs.
How Much CFM Do I Need?
Figuring out how much CFM you need is pretty easy. It’s all about figuring out the air tools you’ll be using with the compressor and determining what CFM those tools require. Then, you’ll probably want to multiply the highest air-tool CFM by 1.5 and get a compressor capable of that CFM.
For example, say the air tool you’ll be using with the highest CFM is an air-powered drill that requires 4 cfm at 90 PSI. Multiply 4 by 1.5 to determine the CFM rating of the air compressor you’ll need. In this case, you’ll be looking for an air compressor capable of delivering 6 CFM at 90 PSI.
Multiplying the highest CFM of the air tools you’ll be using helps to ensure that you’re not always operating the compressor at max capacity. Ensuring you have a compressor capable of delivering more cubic feet per minute than your air tools needs can help prolong the life of the compressor.
To give you a better idea of common air tool CFM ratings, here are some examples.
Air Tools and Their CFM
First, let’s look at some common applications and list their average required CFM range and PSI. Then we’ll list some specific tools and their required cubic feet per minute. Keep in mind that most of these ratings are factored at 25% use, meaning for every minute, the tool is operating for 15 seconds.
- Frame Nailing – Around 2.2 CFM @ 90 PSI
- Drilling – From 3 to 6 CFM @ 90 PSI
- Brad Nailing – 0.5 CFM @ 90 PSI
- Dual Sanding – From 11 to 13 CFM @ 90 PSI
- Mini Grinding – 4 to 6 CFM @ 90 PSI
- Painting – 3 to 11.5 CFM @ 90 PSI
- Sawing – 5 CFM @ 90 PSI
- Angle Grinding – 5 to 8 CFM @ 90 PSI
- Ratcheting – 2 to 6 CFM @ 90 PSI – Varying by size.
|Air Tool||CFM and PSI|
|Framing Nailer||2 CFM @ 90 PSI|
|Drill||4 CFM @ 90 PSI|
|Tire Inflator||2 CFM @ 90 PSI|
|Brad Nailer||0.5 CFM @ 90 PSI|
|Disc Sander||20 CFM @ 90 PSI|
|Speed Saw||4 CFM @ 90 PSI|
|Hammer||4 CFM @ 90 PSI|
|Paint Spray Gun||4 to 8 CFM @ 90 PSI|
Can You Increase CFM on an Air Compressor?
When dealing with any air compressor, there may be a time when you want to increase the CFM. The question then becomes: Can you increase the CFM on an air compressor? And if so, how?
The answer is yes, you can increase the CFM on an air compressor. There are two ways to do this. The first is to purchase another air compressor and connect the two to get more air. However, if you’re going to do this, you’d probably be better off just purchasing an air compressor where the CFM measures higher.
The other way to get higher CFM on an air compressor is to turn down the pressure regulator dial to a lower setting at which your air tool will function. It’s best to do this gradually, ensuring that the compressor runs well before turning it down to the lowest setting. You’ll have to allow the compressor more time to compress air, but it’s a good trade off for many situations.
Understanding how cubic feet per minute relates to your compressor and the use of air tools, and their needed air flow, is essential for getting the correct compressor. And can even be helpful with doing other installations like putting in a new range hood.
But in order to understand CFM, you also need to understand PSI, or pounds per square inch. These two factors affect each other in the use of any compressor. Most compressors for home use have a CFM rating between 0.5 and 5, which is good enough for most DIY home projects and things like filling tires.
Hopefully this article has been helpful in educating you on understanding and determining CFM ratings.