Pressure Tank Calculator
Calculate the right pressure tank size based on pump flow rate, pressure switch settings, and desired cycle rate.
Results
Visualization
How It Works
Pressure tanks store water under pressure so the pump does not cycle on and off with every faucet use. The tank must provide enough drawdown to keep the pump below its maximum cycle rate.
The Formula
Drawdown = GPM x 60 / (Cycles/hr x 2)
Tank Volume = Drawdown / Acceptance Factor
Acceptance = 1 - (Cut-in + 14.7) / (Cut-off + 14.7)
Tank Volume = Drawdown / Acceptance Factor
Acceptance = 1 - (Cut-in + 14.7) / (Cut-off + 14.7)
Variables
- Drawdown — Usable water between cut-in and cut-off
- 14.7 — Atmospheric pressure in PSI (for absolute pressure conversion)
Worked Example
10 GPM pump, 30/50 switch, 6 cycles/hr: Drawdown = 10 x 60 / 12 = 50 gal. Acceptance = 0.309. Tank = 50 / 0.309 = 162 gal. Use 119 gal minimum.
Practical Tips
- Set pre-charge 2 PSI below cut-in with tank empty
- Check pre-charge annually with a tire gauge
- Larger tanks extend pump life by reducing short cycling
- A waterlogged tank (lost air charge) causes rapid cycling