We’re surrounded by hundreds of heating, ventilation, and air conditioning devices in this modern technology-centric life. Both CFM and SCFM are essential metrics to verify the airflow capacity of these HAVAC devices and tools.
Most of these devices come with a specification list of these units. And once I didn’t care about these at all. But after I felt my air compressor wasn’t performing as it should, I started inspecting its ability.
Before troubleshooting an air tool, it’s essential to learn what these units mean, how they are different, in brief, a good understanding of SCFM vs CFM.
With these insights, you can find out whether the manufacturer lies to you about the tool’s capability or not.
Buckle up. In this post, I’ll share all about these metrics in the simplest way.
What’s CFM in an Air Compressor?
CFM stands for Cubic Feet per Minute. It’s the actual measure of airflow through an air compressor in 1 minute in a real-world condition. Basically, it’s the output of the airflow rate of gas or air-driven machines.
For example, if you’ve got an air tool that represents 3 CFM, it means the tool can produce 3ft3 volumetric airflow.
The unit is used to compare the performance of different types of compressors. When it comes to air compressors, the higher the CFM rating is, the more air can be moved through the compressor in one minute.
Unlike SCFM, there is no temperature, humidity, or pressure metrics in CFM. Instead, it comprises air capacity or volume.
What’s SCFM on Air Compressor Ratings?
The SCFM or Standard Cubic Feet per Minute rating is a measure of a compressor’s ability to produce static air pressure under a certain temperature, humidity, and pressure condition.
When comparing airflow, it’s not possible to reach a decision without SCFM. Unlike CFMs, SCFMs consist of some variables. You can figure out total gas (n), air volume (V), temperature (T), and pressure (P) with the help of SCFM.
Most of the air-driven tools manufactured in the United States have an ASME (American Society of Mechanical Engineers), which is considered the standard specification of the following metric.
Generally, the temperature range can be anywhere from 60-degree Fahrenheit to 68-degree Fahrenheit. The standard humidity level to calculate SCFM is 36%.
In terms of air pressure, 14.7 psi (1 atm) is a common matric. Besides, there is a 0.075 lbs./ft3 of air density in this consideration. Though people use 1 atm (standardized atmosphere) in the typical calculation, it doesn’t remain the same in all cases.
“Among the above variables, the humidity and air density are used to calculate the total air volume.”
CFM vs SCFM – Main Differences with Comparison Table
To get a quick understanding of the differentiation factors of CFM and SCFM, check out the below chart.
|Elaboration||Cubic per Minute||Standard Cubic per Minute|
|Standard Temperature (Ts)||CFM doesn’t consist of standard temperature.||SCFM includes the standard metric of temperature, which is 68-degree Fahrenheit.|
|Standard Pressure (Ps)||There is no standard pressure condition in CFM. However, it’s usually calculated with less than 90 psi.||SCFM always has a standard pressure level of 14.7 psi.|
|Relative Humidity||Since CFM is based on real-world conditions, the humidity level considered to calculate the unit is inconsistent.||A standard percentage of humidity is considered to estimate SCFM. It’s 36%, following the ASME.|
|Calculation Flexibility||It’s comparably straightforward to calculate CFM from SCFM.||Without the presence of airflow temperature and pressure, it’s not possible to convert SCFM from CFM.|
How Do You Convert SCFM to CFM?
There is an interesting relation between both units. You can always calculate the CFM out of SCFM. But the reverse is only possible if you’ve got the following variables:
- Temperature of the airflow (ex: 68-degree Fahrenheit)
- Pressure of the airflow (ex: 1 atm)
If you got an air tool with a capacity of 350 SCFM airflow, let’s see how you can easily get the CFM out of it.
Assuming the following values of each required variable of your tool,
- SCFM airflow = 350
- Pressure = 15 psi or 1 atm.
- Temperature = 60-degree Fahrenheit
The formula for calculating CFM from SCFM is,
CFM = SCFM × (Standard Pressure ÷ Actual Pressure) × (Actual Temperature + 459.67) ÷ (Standard Temperature + 459.67)
Let’s just put the values in the following formula.
CFM = 350 × (14.7 ÷ 15) × (60-degree Fahrenheit + 459.67) ÷ (68-degree Fahrenheit + 459.67)
So, the CFM will be = 527.67
“I’ve considered the standard temperature to 68° F. following the ASME rules. You can change it depending on your tool’s manufacturing country.”
How Do Your Calculate CFM on Air Compressor?
Getting CFMs from SCFM is relatively easy. But finding the actual CFM requires multi-stage measures. In order to calculate the CFM on your air compressor, follow the below steps.
Step 1: Find the Gallons per Cubic Foot
To get started with the CFM calculation, first, you need to measure the tank in gallons per cubic foot. It’s supposed to be present on the label of the compressor. For an accurate measurement, use this formula:
Total Gallon = Tank Volume ÷ Gallon per Cubic Foot (each cubic foot is equivalent to 7.48)
Total Gallons = Tank Volume ÷ 7.48
Step 2: Measure the Air Pressure During Refilling
Afterwards, release the excess air from your compressor. When the tank is empty, refill it. Inspect the refilling time and write it down in seconds on paper. Also, note the pounds per square inch (PSIG) when the machine kicks in and out.
You’ll need to deduct the kick-in PSIG from kick-out PSIG. If the kick-in PSIG is 60 and the kick-out PSIG is 80, the result would be 20 PSIG.
After you get the PSIG of your air compressor, you need to calculate the additional air pressure during the refilling process. To do that, divide it by standard air pressure or 14.7 psi. For example, if the PSIG is 20,
(20 ÷ 14.7) = 1.37
Step 3: Identify Total Cubic Feet
Now multiply the previously found total gallons per cubic foot (calculated in step 1) by this additional air pressure during refilling (found in step 2). The result you get is the total pumps in cubic feet by the air compressor during the filling.
Step 4: Calculating the CFM of an Air Compressor
At the final stage, you’ll get the CFM. Divide the total pumps in cubic feet by the time it took to refill the tank (in seconds). And then you’ve to multiply the output by 60. The final output is the CFM of your compressor.
What’s a Good SCFM For Air Compressor?
As the SCFM refers to the air pressure capacity in a standard condition, having a higher rating means the stronger your air compressor is. However, in air-driven tools, there are different ratings of SCFM and PSI depending on the tool’s type. Check out the below chart to find what SCFM you need.
|Random Orbit Sander||90||6 to 15|
|Spray Gun||30 to 50||7 to 12|
|Framing Nailer||70 to 120||4 to 5|
|Ratchet||60 to 100||4|
|Finish Nailer||70 to 120||2 to 3|
|Brad Nailer||70 to 120||1 to 3|
|Stapler||70 to 120||1 to 3|
|Pin Nailer||60 to 100||1 to 2|
Frequently Asked Questions
1. How many CFM do I need for air tools?
Unlike heavy HAVAC, most air-driven tools are manufactured for light jobs. Besides, these are mainly powered by portable air compressors.
The adequate CFM for these tasks is less than 5, while the psi or pound per square inch should be anywhere from 70-90.
If you’re using a more powerful air tool, the CFM should be more than 10, whereas the psi range should be 100-120.
2. How much SCFM do I need to run air tools?
The SCFM, in terms of air tool, is almost similar to the CFM measure. For smaller tools or lighter jobs, it ranges between 0-5 SCFM. And when it comes to heavier jobs, or you’re operating a bigger tool, it should exceed 10 SCFM.
To get more accurate SCFM settings, you can multiply your gear’s ratings by 1.5. The result you get is the minimum Standard Cubic Feet per Minute of your air tool.
3. Is higher CFM better?
Whether you need a higher or lower CFM depends on the type of job you want to accomplish and the tool you’ve purchased for the purpose. Higher CFM means the tool will get a high rate of air pressure from your compressor, which might be good for heavier jobs.
That was a complete breakdown of SCFM vs CFM in the easiest way. Basically, both represent the air pressure capacity of your compressor in standard and actual conditions, respectively.
Having a good knowledge of these units can help you examine whether your air compressor is working correctly or not.