The right pressure tank size depends on your pump GPM and pressure switch setting. Use this chart as a starting point — then use our calculator for a precise result.
| Pump GPM | 30/50 Switch | 40/60 Switch | Recommended Size |
|---|---|---|---|
| 5 GPM (1/2 HP) | 14 gal | 11 gal | 20 gal |
| 7 GPM (3/4 HP) | 20 gal | 16 gal | 32 gal |
| 10 GPM (1 HP) | 28 gal | 22 gal | 44 gal |
| 15 GPM (1.5 HP) | 42 gal | 34 gal | 60 gal |
| 20 GPM (2 HP) | 57 gal | 45 gal | 86 gal |
💡 Always go larger than the minimum. The minimum size prevents short cycling under ideal conditions. In real use — multiple fixtures running, peak demand periods — a larger tank provides better protection for your pump.
Your pump's GPM rating is on the nameplate on the pump motor or in the original documentation. If you don't know it, a 1/2 HP pump typically delivers 5–7 GPM, a 3/4 HP delivers 7–10 GPM, and a 1 HP delivers 10–15 GPM. These are approximations — use the calculator for a precise result.
An undersized tank forces the pump to short cycle — turning on and off every few seconds. Each motor start draws 3–5x normal amperage, overheating the windings. A correctly sized tank is the single best investment in pump longevity.
Tank drawdown (the water actually available between pump cycles) = approximately 30% of total tank volume for a bladder tank. A 44-gallon tank provides about 13 gallons of drawdown. This is why nominal tank size is larger than the actual usable water storage.
A 1 HP pump typically delivers 10-15 GPM. Based on the chart above, that calls for a minimum of 22-42 gallons depending on your pressure switch setting, with a 44-gallon tank recommended for comfortable margin. Use the calculator above for a result based on your exact GPM.
Yes, and it is usually a good idea. A larger tank only improves performance: longer pump run times, fewer cycles, and more stored water during peak demand. The only downsides are higher upfront cost and more floor space. There is no real ceiling on going bigger, unlike going smaller.
An undersized tank forces the pump to short cycle, turning on and off every few seconds or minutes instead of every several minutes. Each start draws several times the pump's normal running amperage, which heats the motor windings and wears out the pressure switch contacts. Over time this can cut a pump's lifespan from 15 years down to 3-5 years.
Yes. A 30/50 switch has a wider pressure swing than a 40/60 switch, which means more usable drawdown per gallon of tank size. That is why the chart shows a smaller minimum tank size for 30/50 systems than for 40/60 systems at the same pump GPM.
Check the nameplate on the pump motor itself, which usually lists GPM directly or at minimum the horsepower and amperage you can cross-reference. If the nameplate is unreadable, a rough estimate based on horsepower (covered above) is enough to get a usable result from the calculator.
An undersized tank causes low pressure, short cycling, and early pump failure. Check yours free in 2 minutes.
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