To calculate the CFM (Cubic Feet per Minute) for an air compressor, follow these steps:
Preparation
1. Ensure your air compressor tank is empty.
2. Have a stopwatch or timer ready.
3. Note the volume of your compressor tank in gallons.
Calculation Process
Step 1: Measure Fill Time at Different PSI
Turn on the compressor and time how long it takes to fill the tank at 40PSI, 90PSI, 100PSI & 150PSI. You can do it in one pass, just need to note the time at every increment.
Step 2: Determine CFM
Take the volume in gallons then divide by 7.5 times the pressure recorded at divided by 15 divided by the time it took to reach that pressure (note you have to calculate the time in decimal for the seconds).
Formula
The simplified formula for CFM calculation is:
CFM = Tank Volume in gallons / 7.5 * Pressure you want the CFM at / 15 / (Fill Time in minutes and decimal)
Example
Let's say you have a 120-gallon tank that fills from 0 to 150PSI in 2 minutes 8 seconds.
1. Tank Volume: 120 Gallons
2. Pressure measured at: 150PSI
3. Pump time: 2.1333 (8 seconds = .1333 in decimal)
4. CFM: 120 / 7.5 * 150 / 15 / 2.1333 = 75 CFM
Therefore, this compressor has a CFM rating of approximately 75 CFM at 150 PSI.
Remember that actual CFM can vary based on factors like temperature and humidity, so this calculation provides an estimate of your compressor's performance.