Pressure Tank Size Calculator
Estimate drawdown, pump run time and the nominal tank size you need from your pump flow and pressure settings.
Your system
gpm
psi
psi
psi
Leave blank to use cut-in − 2 (38 psi)
gal
min
Longer run times reduce pump wear from short cycling.
Drawdown
11.3 gal
25.8% of a 44-gal tank
Run time per cycle
1.1 min
For the entered tank volume
Tank needed for target run time
39 gal
Nominal volume for 1 min at 10 gpm
Pre-charge used
38 psi
≈ cut-in − 2
How this is calculated
Drawdown uses Boyle’s law for the trapped air at absolute pressure: drawdown = tank volume × pre-chargeabs × (1/cut-inabs − 1/cut-outabs), where abs adds atmospheric pressure (14.7 psi). Manufacturers’ published drawdown may differ slightly due to tank geometry — confirm against the spec sheet before buying.
This is an estimate, not a specification
Results are for orientation only and depend on the accuracy of your inputs and assumptions. They do not replace a professional assessment, a manufacturer’s performance data, or laboratory testing. See our disclaimer.