Estimate air compressor pump-up time to fill a tank from its size, CFM and start and cut-out pressures, or solve air volume, flow or time with V = Q × t.

Constant-flow volume transfer. Add start and cut-out pressures below to estimate tank pump-up time.

For a tank fill, enter the tank size plus the pressures below. Otherwise use free-air volume on the same basis as the flow.

Tank fill (pump-up) pressures
Tank pressure when filling starts; 0 for an empty tank.

Related Calculators

Compressor Time Formula

The compressor time calculator uses the relationship between tank volume, flow rate, and time. The calculation assumes the volume and flow rate are expressed on the same basis, then converts units as needed.

t = V / Q
  • t = time
  • V = air volume on the same pressure and temperature basis as the flow rate
  • Q = flow rate

To calculate the missing value, the same formula can be rearranged:

V = Q × t
Q = V / t
  • V = tank volume, in gallons or liters
  • Q = flow rate, in CFM or L/min
  • t = time, in minutes or hours

The calculator converts all inputs to base units before calculating: liters for volume, liters per minute for flow rate, and minutes for time.

  • Calculate time: enter tank volume and flow rate. The calculator divides volume by flow rate.
  • Calculate tank volume: enter flow rate and time. The calculator multiplies flow rate by time.
  • Calculate flow rate: enter tank volume and time. The calculator divides volume by time.

Common Compressor Unit Conversions

These rounded conversions are shown for reference. The calculator uses 3.785411784 L per US gallon and 28.316846592 L per cubic foot.

Measurement Conversion
Gallons to liters 1 gallon = 3.78541 liters
Liters to gallons 1 liter = 0.264172 gallons
CFM to L/min 1 CFM = 28.3168 L/min
Hours to minutes 1 hour = 60 minutes

Typical Air Compressor Tank Sizes

Tank Size Common Use
1 to 6 gallons Small nailers, inflating tires, light-duty portable use
8 to 20 gallons Garage tools, intermittent air tool use
30 to 60 gallons Shop compressors, longer tool runtime
80 gallons or more Larger stationary systems and higher air demand

Example Compressor Time Calculations

Example 1: Calculate time from tank volume and flow rate

You have a 20 gallon tank and a flow rate of 5 CFM.

Assuming the volume and flow use the same pressure and temperature basis, convert the volume to liters:

20 gal × 3.78541 = 75.7082 L

Convert the flow rate to liters per minute:

5 CFM × 28.3168 = 141.584 L / min

Now divide volume by flow rate:

t = 75.7082 / 141.584 = 0.5347 min

The time is about 0.5347 minutes, or about 32.1 seconds.

Example 2: Calculate flow rate from tank volume and time

You have a 50 liter tank and it takes 4 minutes.

Q = 50 / 4 = 12.5 L / min

The flow rate is 12.5 L/min. If you select CFM, that is:

12.5 / 28.3168 = 0.4414 CFM

FAQ

Does this calculator account for pressure?

Only when you enter them. In the time mode, add the start and cut-out pressures to estimate tank pump-up time with t = V × (P2 − P1) ÷ (Patm × Q), where Q is the compressor's free-air delivery. Temperature, compressor efficiency and pressure drop are not included.

Why does CFM need to be converted?

CFM is cubic feet per minute, while the calculator uses liters per minute internally. Since tank volume may be entered in gallons or liters, the calculator converts all values to consistent base units before solving the formula.

What should I enter if I want to calculate the missing value?

Choose the value to calculate, then enter the other two values and their units. For example, choose time and enter air volume and volumetric flow rate on the same pressure and temperature basis.