Fill up your compressor, then slowly release the air to the point where the compressor kicks in again. Take note of the amount of psi (starting psi value) on the compressor's tank gauge at this time and hit your stop watch to time the amount of time it takes for the compressor to reach its max pressure and it kicks out again. Look at your tank gauge again and here you will have your finished psi value.

Note: the starting psi is where the compressor kicks in when tank pressure drops below the regulator pressure . The finished psi value is the factory set, maximum allowable pressure the tank can hold.

Example:

Compressor starts up at 90 psi (starting psi) runs for 1 minute and 1 seconds and kicks out at 140 psi (finished psi value)
1 minute and 1 secs = 61 seconds, the amount of the time value.

The Calculation

1. enter tank size measured in gallons
2. starting psi value (compressor kicks in after tank pressure drops below the set pressure)
3. finished psi value ( maximum allowable working pressure)
4. the time it takes from starting to finished psi values

The Results

1. The cfm's your compressor can deliver at the starting psi value.
2. Cfm conversion to litres per minute