SettingsSettings for this calculationUS
Your well pump's rated flow rate.
Check the pump's nameplate or the well driller's report.
The shortest the pump should run per cycle to avoid premature wear.
Many pump manufacturers recommend at least 1 minute of continuous run time per cycle to prevent motor overheating from short-cycling.
Recommended tank size
30.3 gal
Actual drawdown fraction varies by tank precharge pressure and your specific pressure switch cut-in/cut-out settings — check your tank manufacturer's drawdown chart for a precise figure.
- Required drawdown
- 10 gal
They open the calculator with your figures already in it
Well Pressure Tank Sizing Calculator: 30.3 gal — shown in imperial, US market. The link sets both, so the result they see is the one on your screen.
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How this was calculated
Formula source(s)
- Required drawdown = pump flow rate × minimum recommended cycle time (minutes); recommended tank size = required drawdown ÷ typical drawdown fraction (~33% for a standard captive-air tank)
Inputs used
- Pump Flow Rate
- 10 gal/min
- Minimum Pump Run Time (minutes)
- 1
Intermediate steps
- Required drawdown
- 10 gal
Confidence note: Actual drawdown fraction varies by tank precharge pressure and your specific pressure switch cut-in/cut-out settings — check your tank manufacturer's drawdown chart for a precise figure.
What this calculation does not cover
- The 33% usable fraction is a fixed assumption, not something this calculates. Real drawdown depends on the tank's air precharge and on your pressure switch's cut-in/cut-out settings, and the usable fraction shrinks as the switch band moves higher — so a tank set up at a high pressure band delivers less than this assumes. Check the manufacturer's drawdown chart for the model and switch setting you are actually running.
- It treats the pump's rated flow as a constant. A pump's delivered flow changes with the head it is working against and rises and falls across the cut-in to cut-out band, so the flow moving through the tank over a real cycle is not the nameplate figure this uses.
- This sizes a tank against pump cycling and nothing else. It does not look at the well's yield or recovery rate, or at peak simultaneous household demand — a tank large enough to stop short-cycling can still be far too small for a low-yield well or a heavy draw, and that is a storage problem this rule does not address.
- The fixed fraction describes a captive-air tank (bladder or diaphragm). It does not apply to a galvanized air-over-water tank, whose air charge dissolves into the water and needs periodic recharging, nor to a constant-pressure or VFD system, which is deliberately paired with a small tank and is not sized this way.
- This is not an installation specification. It says nothing about the tank's pressure rating against the relief valve setting, the stand or floor loading, freeze protection, the tank tee and pipework, or the well and plumbing code requirements that govern the installation.
Estimated cost — your price
This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.
Computed in your browser — nothing you enter is uploaded. Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.
Sources checked 2026-09-02 · in the site-wide review of 2026-09-06 · v1.1.1
Regulatory standards & verification citations1
- Required drawdown = pump flow rate × minimum recommended cycle time (minutes); recommended tank size = required drawdown ÷ typical drawdown fraction (~33% for a standard captive-air tank)
Cite this page
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