Air Compressor Fill Time Calculator: Pump-Up & Recovery Time

Enter your tank size, the compressor's output and the pressure switch settings, and this tool estimates how long the pump runs to fill an empty tank and how long it takes to recover between cut-in and cut-out. If your compressor seems to run forever, this is how you tell whether that's normal or a sign of a worn pump or a leak.

The math is simple: a tank holds far more air than its physical volume because the air is squeezed in. Raising the pressure inside the tank takes a fixed amount of free (atmospheric) air, and your compressor delivers that free air at a set number of cubic feet per minute. Fill time is just the air needed divided by the air delivered.

How the numbers work

To fill a tank from empty to its cut-out pressure, the pump has to push in roughly tank volume in cubic feet, times cut-out pressure, divided by 14.7 (atmospheric pressure in PSI). One gallon is 0.134 cubic feet. Recovery time between cut-in and cut-out uses the same math but only across the pressure band the switch cycles over, which is why a compressor with a narrow band cycles on and off more often but recovers quickly.

A reality check on CFM

Most compressors are rated in CFM at 90 PSI, but real delivery falls as tank pressure climbs toward cut-out, so treat these figures as a best-case estimate. If your actual fill time is much longer than the tool predicts, the usual suspects are a worn pump or piston rings, a leaking tank check valve, a bleeding-down pressure switch unloader, or air leaks downstream. If it is close, your compressor is healthy.