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The terminology and jargon used on an air compressor can be a bit confusing. The first problem most people encounter when comparing different air compressors is SCFM (standard cubic feet per minute).
What is SCFM on an air compressor, anyway? And adding to the confusion, tools are generally rated in CFM (cubic feet per minute) and PSI (pounds per square inch). So, what’s the difference between these two technical units for measuring gas?
Let’s break all of these critical measurements for air compressors down to better understand what you need and what your compressor can do.
Table of Contents
- What Is SCFM?
- What Is CFM?
- What Does 2.6 SCFM 90 PSI Mean?
- What Is SCFM vs CFM? The Differences
- SCFM vs CFM in Evaluating an Air Compressor
- How Much SCFM Do I Need to Run Air Tools?
- What Does the Volumetric Flow Rate for Air Compressors Mean?
- What Does the Pressure for an Air Compressor Mean?
- What Is SCFM vs CFM
- An Engineering Perspective on SCFM
- FAQs (Frequently Asked Questions)
What Is SCFM?
If you’ve ever shopped for or researched air compressors, you already know that SCFM is one of the essential terms to understand. Air compressors are rated for a specific SCFM, and knowing what SCFM you need is vital to getting an air compressor suitable for your required applications.
What Does SCFM Stand For? SCFM Meaning
SCFM is the standard cubic feet per minute of air that an air compressor can process.
However, more important than simply defining what the letters mean is understanding why it’s so important. The SCFM is a vital measurement for understanding what your air compressor is capable of. Using the SCFM, you can figure out what sort of tools you can run and how many of them.
What Is SCFM on an Air Compressor?
The “standard” in SCFM refers to the standards against which the compressor is compared. You can’t compare two units to one another unless the air they are pumping is identical. The Compressed Air & Gas Institute (CAGI) and the American Society of Mechanical Engineers (ASME) have established “standard conditions” as 14.7 PSI (atmospheric pressure), 68 degrees Fahrenheit, and 36 percent relative humidity at sea level.
As SCFM is measured at these standard conditions, it allows the measurement of mass flow rate. Mass flow rate is the amount of substance or particles that pass through a surface at a specific unit of time.
For air compressors, SCFM is the agreed-upon measure of the overall power of a compressor. As described above, this standard helps you compare one compressor to another. As SCFM is a measure of air volume. The bigger and more powerful your air compressor is, the higher the SCFM rating is.
What Is CFM?
So, what is CFM? It’s the usual unit of measure for the volume of discharge air from a compressor over time. As you may have guessed, its units are based on; volume/time. CFM is the acronym for cubic feet per minute. A compressor has a specific number of cubic feet of compressed air per minute (CFM) of flow from its discharge port.
For more on what is CFM and what does CFM mean on an air compressor please visit our guide. If you’re wondering how to increase CFM on your air compressor, we also have a detailed guide!
What Does 2.6 SCFM 90 PSI Mean?
Air compressors are typically rated with an SCFM at a specific pressure. So when a compressor specification says 3.8 SCFM at 90p psi, this means that the air compressor PUMP has the ability to deliver 3.8 SCFM at a regulated pressure of 90 psi.
Some air compressors are rated with 2 different SCFM ratings i.e:
- 3.1 SCFM at 90 psi
- 4.2 SCFM at 40psi
This basically means that the COMPRESSOR PUMP can produce 3.1 SCFM at 90 psi, but it can increase slightly more SCFM (4.2) at 40 psi.
This is a cause of MUCH confusion. Once again, the compressor manufacturers are referring to the rating of the COMPRESSOR PUMP. The SCFM and pressure you get at the outlet of the air tank are only related in terms of the ability of the compressor pump to replenish the air used. i.e. if you use 8 SCFM at 90 psi from a compressor that’s rated at 3.1 SCFM at 90 psi, your air tool will work until you drain the air tank and the compressor pump has a chance to catch up.
See our detailed guide on how to calculate SCFM of an air compressor to understand how the relationship between SCFM and psi on your compressor is completely different if talking about the compressor pump vs the air tank outlet.
What Is SCFM vs CFM? The Differences
Well, the simplest way to think about CFM vs SCFM is to divide the two terms up. The difference between SCFM and CFM is that SCFM is more indicative of how the air which is pressurized to a standard value will perform when delivered to the air tool from the compressor. The air compressor CFM is more relevant to the internal capacity of an air compressor.
Since SCFM is measured at these hypothetical standard conditions mentioned above, chances are your real-world CFM is different. If you measure what the machine is actually doing, the measurement is known instead as ACFM or, actual cubic feet per minute.
SCFM vs CFM in Evaluating an Air Compressor
While the air compressor is measured in how much air it can compress in a given minute, tools are rated by how much air they need to operate. Tools will be rated in both PSI (pounds per square inch of air pressure) and in SCFM.
Manufacturers provide the CFM and SCFM ratings of their air compressors or tools measured at sea level. SCFM gives us an air compressor’s volumetric flow rate at a standardized condition while there are no real standards for CFM.
Is SCFM Higher Than CFM?
Yes, CFM ratings are commonly lower than SCFM ratings… The air compressor CFM rating comes after the air is pressurized, typically maintained at 90 PSI, therefore this results in a smaller air volume.
On the flip side, as you know now, air compressor manufacturers expand the air to a standard condition while taking into account the variables mentioned. This standard condition has a significantly lower pressure (14.7 PSI), therefore the volume is bigger and thus SCFM is always a greater number than CFM.
How Much SCFM Do I Need to Run Air Tools?
Once you understand the difference between the theoretical SCFM and CFM measurements, you might be left wondering what to do with all of this information. How does it help you get the right air compressor or the right tool?
In a factory setting, where near-continuous use of the pneumatic system is expected, the best policy is to add up the all the air tools CFM ratings that will be used. You should then compare the total to what is available from the air compressor driving them. Learn more about pneumatic systems here.
Ideally, the air compressor should be providing at least 150 percent of the CFM air tool requirements. That way, there will always be plenty of reserve power in the system.
For home use, you do not have to invest in quite so much reserve power. But you still need to compare the numbers to ensure that you can use the tools you want to, as often as you want to, without exceeding the compressor’s duty cycle.
Here’s an example… Your air nailer needs 4 to 6 CFM of compressed air flow at a certain pressure to operate correctly. Most nailers and air tools require between 60 and 100 PSI. The stated air consumption for the nailer is likely based on the air tool running continuously.
If you need to use the air nailer continuously, you will need a compressor that will continuously deliver at least 4 to 6 CFM. But with air nailers, spot use is more prevalent than continuous use.
For more information on how to size an air compressor please check out our article covering this topic.
What Does the Volumetric Flow Rate for Air Compressors Mean?
The volume flow rate is defined as the amount of fluid that passes through a link in an air compressor at any given moment. Think about the volume of air flowing between different components within an air compressor system in cubic feet per minute it takes for this newly pressurized air to travel from the tank to the endpoint application.
In air compressors, the volume flow rate is very important because it gives you an indication of the amount of pressurized air that can pass per second through the air compressor and its attached air tools. This volume flow rate will indicate whether or not it is possible to deliver a certain volume of air to your endpoint application in a split second.
Length of pipe, number of attachments, setup, and leaks are just a few of the factors that can affect the volumetric flow rate.
What Does the Pressure for an Air Compressor Mean?
The volumetric flow rate is not the only measurement you’ll need to pin down with your air compressor. It’s also important to understand the pressure, PSI, or pounds per square inch.
PSI refers to the amount of air pressure being delivered through an air compressor per inch. The vast majority of pneumatic tools require PSI ratings in the range of 40 to 90 psi to ensure successful operation. The higher the pressure, the more power the tool has to operate.
By clarifying how much pressure and SCFM you need for your application or air tools, you can then establish the pressure and SCFM specifications for your air compressor. For more on this, see my article on what size air compressor do I need?
PSI and CFM have an inverse relationship… meaning as there’s an increase in pressure, the CFM decreases and vice versa. This is true at the OUTLET of the compressor tank – but not necessarily true for the compressor pump itself. See my detailed article about increasing the CFM of your compressor to understand the difference.
When figuring out the total required CFM and PSI needed for a project, it’s important to keep in mind the compressor’s duty cycle. Many smaller compressors are not built to run continuously. Therefore, it cannot continuously deliver compressed airflow at the specified pressure or volumetric flow rate on a non-stop basis.
What Is SCFM vs CFM
|Name||Standard Cubic Feet per Minute||Cubic Feet per Minute|
|Standards||Standard temperature, pressure, and volume at which SCFM must be calculated||No standard conditions at which CFM must be calculated|
|Calculation||To calculate SCFM values, the air is expanded to its standard condition of around 14.7 PSI (atmospheric pressure)||To calculate CFM values, the pressure is maintained at or below 90 PSI|
|Measurement||SCFM is always a bigger number than CFM because it has a larger air volume due to being calculated at a lower pressure||CFM is always a smaller number than SCFM because it has a smaller air volume due to being calculated at a higher pressure|
|Relevance||SCFM is more relevant to how the pressurized air at a standard value will perform at the air tool||CFM is more relevant to the internal capacity of the air compressor|
Above is a comparison table between SCFM and CFM drawn from the information provided in this article.
Do you have a question about the difference between SCFM and CFM or air flow rates? Please add your comment here (along with photos if applicable) to help others help you with your compressor and equipment problem!
An Engineering Perspective on SCFM
The following is a contribution from a visitor… a consideration of SCFM from an engineer’s perspective. I appreciate the information and am happy to share this with visitors.
“Using SCFM provides a more precise measurement of airflow.
Air gets denser as you compress it, and less dense as you heat it. In order to provide accurate flow measurement to an end-user or to provide an “apples to apples” comparison of flow, that variability has to be removed.
So a “standard” cubic foot was created – based as you’ve said – rather loosely on a standard pressure and temperature.
Typically being 1 atmosphere and temperature of either 60F, 68F, or 15C. In other words, 1 SCF is the space that 1 cubic foot of air occupies at atmospheric pressure and a standard temperature. At 90 PSIG that same cubic foot takes up a lot less space than it did at atmospheric pressure so 1 CFM @ 90 psi contains 7 SCF (standard cubic feet).
In real life, CFMis the useful output rate and it is a measure of exactly how many cubic feet leave the compressor at the rated pressure in a minute. There is no regard for the density of that cubic foot or whether or not my compressor’s cubic foot contains as much air as your compressor.
That’s where SCFM comes in – it equalizes the playing field, providing standardized correction to capacity claims at 110 PSIG versus those at 90 or 150 PSIG for instance.
In reality, no one using compressed air to drive a tool really cares about SCFM – we’re all concerned about how many CFM at my required pressure can I get, so, I know I can drive this air wrench, etc. As long as I get 30 CFM of 90 psi air and my wrench works I don’t care how many SCF that air contains.
However, if you deal with the accounting side of a large firm you’ll know they bill or pay based on SCFM used so that every cubic foot used is corrected for pressure and temperature, preventing over or undercharging. It provides consistency day to day and season to season – same goes for the gas company, your bill will show used in SCF (perhaps 1000’s of SCF).”
FAQs (Frequently Asked Questions)
To convert SCFM to CFM you will need to know the pressure (in psi) and temperature (in °F) you’re calculating the CFM at, and then use the ideal gas law. Visit our how to calculate SCFM guide!
The difference between SCFM and CFM is that SCFM is more indicative of how the air which is pressurized to a standard value will perform when delivered to the air tool from the compressor. The air compressor CFM is more relevant to the internal capacity of an air compressor. Simply put, SCFM is a measure of airflow at exactly 1 atm pressure.
SCFM is always a bigger number than the CFM as it is calculated at a lower pressure than CFM. To calculate CFM values, the pressure is maintained under 90psi. To calculate SCFM values, the air or gas is expanded to a standard condition which is around 14.7psi. The lower the pressure, the greater the volume!
4 SCFM on an air compressor means that at standardized conditions, the compressor is capable of providing 4 cubic feet of air per minute.
Additional CFM reading:
- SCFM Vs ACFM Vs ICFM – What’s The Difference? Converting & Calculating
- Best Ways to Increase CFM On Air Compressors
- Connecting Two Air Compressors Together
- How to Calculate CFM of Air Compressors
- CFM Pipe Size Chart
- What Is CFM and What Does CFM Mean on An Air Compressor?
- Air Compressor Size For Spraying Stucco & Plaster
- Does a die grinder require low or high CFM?
- Speedaire 4B247 swapped with 2Z499 and its effect on CFM?
- 20 CFM Air Compressor – Buying, Hiring, What Can They Run?
- Air Compressors That Produce 500 CFM And Above
- CFM SCFM PSI Compressor Flow Issues
- Ingersoll Rand Type 30 model 242 HP and CFM?
- CFM rating of Black Max compressor
What size air compressor:
- What Size Air Compressor Do I Need? How to Size An Air Compressor
- What Size Air Compressor Do I Need For Impact Wrench?
- What Size Air Compressor For Sander?
- What Size Air Compressor For Sandblasting?
- What Size Air Compressor For Framing Nailer?
- What Size Air Compressor For Air Hammer?
- What Size Air Compressor For Air Ratchet?
- What Size Air Compressor for Car Detailing?
- What Size Air Compressor for Truck Tires?
- What Size Air Compressor For Nail Gun
- What Size Air Compressor for Painting Cars?
- What Size Air Compressor Do I Need for Spray Painting?
- What Size Air Compressor For Staple Gun Or Upholstery Air Stapler?
- What Size Air Compressor For Sandblasting?
- What Size Air Compressor Do I Need For A Die Grinder?
If you have any questions regarding CFM vs SCFM, please leave a comment below, with a photo if applicable, so that someone can help you!
I think my question is a little different. I have a Bostitch 6 gallon, 2.6 [email protected] psi compressor. I’d like to buy an air impact wrench I can use with it for home auto work such as removing/installing lug nuts, etc. Most of the impact wrenches I’ve seen require much more CFM than that, but I understand some will still work OK with this compressor for very intermittent use, such as the sort of home auto chores I anticipate. Some are 3/8″, some are 1/2″. So if I’m trying to find an impact wrench that I can use with this… Read more »
You’re talking cars, not SUVs? You may be able to away with a relatively low torque (100 or so foot pounds) with that. My compressor is a bit larger, but I (normally) have no trouble getting 5 or six lugs off before I run out of torque. In the time it takes to do whatever, the compressor is recharged and I can do the next wheel. If you find you can’t get a wheel off, and want to get it off without waiting on the compressor, you can add a 5 or 6 gallon portable tank. You’ll have to wait… Read more »
Doug – Thanks a lot for the thoughts.
Yep. Talking about cars & (mostly) about lug nuts, sometimes others. Any thoughts about 3/8″ vs. 1/2″ drives for this? Any specific impact wrench suggestions?
1/2. You may not need it often, but if you can get what little air you in it fast enough, you’ll have the torque you may need that you couldn’t get from 3/8. I got mine in a kit I bought years ago, so no real reccomendations, but if you have a HFT nearby, I’d go with one of theirs. Try to beat it up soon after you buy it, so if it’s going to break it does it while under warranty. I find *most* of their stuff is pretty good, especially for the $. And that includes their sockets,… Read more »