Cubic feet per minute (CFM) is an essential parameter of all air compressors, determining what tools you can operate.
An air compressor CFM calculator takes into account the volume of the tank, desired pressure, fill-up time, and operational factors to estimate the airflow of the compressor. Most air compressors mention their CFM in the manual. However, you may still need to calculate it for older compressors.
The following sections will define CFM and cover how to calculate the CFM of a compressor.
How to calculate the CFM of a compressor?
Before we cover how our air compressor CFM calculator works, let’s first discuss why you need to do that in the first place.
The reasons to calculate the CFM of a compressor include:
- Verifying the CFM mentioned on your air compressor
- Monitoring the efficiency of an air compressor over time
- Determining when to buy a new motor for your air compressor
Our air compressor CFM calculator takes into account several factors to estimate airflow. In reality, calculating CFM is subject to complex equations and a number of variable factors. Therefore, CFM calculators only give you a close approximation. Luckily, the calculated figure will be close to the real one, allowing you to objectively assess your compressor’s efficiency.
Importance of air compressor CFM
The importance of CFM lies in determining the efficiency of the motor and whether it’s still compatible with specific applications.
As you may know, each pneumatic tool has a target CFM required by the air compressor. For example, light-duty die grinders require a compressor able to generate 3 to 5 CFM. When the CFM of your air compressor drops, the productivity of your die grinder applications will also decrease.
Factors that impact air compressor CFM calculators
Calculated CFM uses a simplified model that has a few limitations. For instance, it doesn’t account for some factors that may have an impact on real-world performance. However, these limitations are insignificant for consumer-oriented compressors.
With that said, here are some factors that impact air compressor CFM calculations:
1. Efficiency of the motor
The efficiency of your air compressor is the first factor that CFM calculators don’t consider. Each manufacturer claims that its products are highly efficient. In reality, air compressor efficiency declines in almost all motors. However, it may occur at a different rate from one brand to another.
2. Ambient temperature
High temperature decreases the density of air. As a result, it will affect the airflow (i.e., CFM) delivered by the compressor. Thankfully, the impact of temperature fluctuations on CFM calculations is negligible.
3. Compressor type
The last factor that’s neglected by CFM calculations is the type of compressor. As a rule of thumb, rotary screw compressors tend to deliver consistent CFM due to their continuous operation. [1]
Luckily, you can account for this factor by calculating the CFM of your compressor several times at different pressures.
Units of air compressor CFM calculator
Tank volume
Our air compressor CFM calculation formula uses cubic feet to measure tank volume. To conduct this calculation, we need a conversion factor of 0.132 (1 gallon in cubic feet). Fortunately, you don’t have to worry about this conversion. You can submit the size of your air tank in gallons, and our CFM calculator will take care of the rest.
Pressure unit
Pounds per square inch (PSI) is a standard unit used to calculate CFM. Make sure to submit the desired pressure of operation in PSI when using our CFM calculator.
For example, air impact wrenches require between 90 and 120 PSI to operate. Therefore, you need to submit that specific pressure level. [2]
Time unit
Most air compressor CFM calculators use seconds as a unit of time. This conversion is important to maintain consistent CFM calculations over time. Rounding the pump-up time to minutes and neglecting the seconds can substantially shift the accuracy of the calculation.
Compare calculated CFM to the manufacturer’s data
Once you compute air flow using our CFM calculator, the next step is to compare the result to the manufacturer’s data. [3]
In general, the CFM provided by the manufacturer is accurate when the air compressor is brand new. After a few years, the efficiency and CFM of the compressor drop significantly.
However, it doesn’t hurt to cross-reference your calculated CFM with the figure specified by the manufacturer. Ideally, you would start calculating CFM when your compressor is still new. This will give you a baseline figure for future calculations.
Common mistakes when calculating air compressor CFM
The most common mistake when you calculate air compressor CFM on your own is unit conversion errors. For example, your air compressor tank is most likely in gallons. However, formal equations use cubic feet to calculate CFM.
Another common mistake is neglecting proper mathematical formatting, which can result in wildly false figures.
To avoid these mistakes, just use our air compressor CFM calculator, which takes into consideration all of these factors.
How to use our air compressor CFM calculator
Using our air compressor CFM calculator is relatively straightforward. All you need is a stopwatch and a few minutes to spare.
Here is the information needed from you:
- Air compressor size (in gallons)
- Desired pressure (in PSI)
- Time to reach desired pressure (in minutes)
For the desired pressure and time, here’s what you need to do:
Open the drain valve (typically located at the bottom of the air tank) and empty the reservoir. After that, use the stopwatch on your smartphone to calculate how long it takes to reach the desired pressure. If you stop the compressor before or after reaching the desired pressure, just copy the number you see on the pressure gauge to the calculator (in PSI).
The figure below demonstrates the steps needed to calculate air compressor CFM:
For example, a typical 60-gallon air compressor takes about 10 minutes to reach 160 PSI. Submitting these figures into our calculator gives you 8.5 CFM.
Air compressor CFM calculator at different pressures
If you intend to use multiple pneumatic tools, this means the desired pressure will change. For example, the CFM of a die grinder is different from a pneumatic saw.
Luckily, our air compressor CFM calculator allows you to measure airflow at different pressures.
Air compressor CFM calculation formula
To accurately measure airflow, we use the following air compressor CFM calculation formula:
CFM = (Tank Volume x Constant Factor (0.536) x Desired Pressure) ÷ Pump-up Time
The table below details each factor of the equation:
| Equation factor | Significance |
| Tank volume | Converted from gallons or liters to cubic feet |
| Constant factor | A formula constant that considers unknown factors |
| Desired pressure | The required pressure in PSI (e.g., 100 PSI for air hammers) |
| Pump-up time | Time required to reach the desired pressure in seconds |
When to seek professional help
Calculating the CFM of compression systems for industries may require more accurate figures. For this reason, relying solely on a CFM calculator may not give you precise measures. [4]
While the difference between calculated and real figures may not be big, this can have significant ramifications on the cost and productivity of the enterprise.
In this case, it is best to seek professional help from a technical team that uses sophisticated tools to provide more precise measurements.
Conclusion
Air compressor CFM calculation is a crucial process that objectively assesses the efficiency of your compressor. Over time, the CFM of all air compressors declines, with varying degrees.
Using our air compressor CFM calculator will save you time and prevent common errors made during calculation.
If you have any feedback about our calculator, please do not hesitate to contact us by clicking here.