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Stop Your Well Pump
From Short-Cycling

The only calculator built specifically to size pressure tank bladders for well water systems. Prevent pump burnout before it costs you $1,200.

$1,200
Avg pump replacement cost
2 min
To size your tank
100%
Free, forever
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Pressure Tank Sizing Calculator

01 — Pump Specifications
GPM
02 — Pressure Switch Settings
PSI
PSI
PRESSURE RANGE PREVIEW
— 40 PSI ON
0 PSI 60 PSI OFF 100 PSI
03 — System Details
GAL
PSI
Results
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Enter your pump specs and pressure switch settings to get your recommended tank size, draw-down volume, and cycle analysis.

Minimum Tank Size Required
—
GAL
Total tank capacity (not draw-down)
Draw-Down Volume
—
Max Cycles/Hour
—
Runtime Per Cycle
—
seconds pump runs each cycle
Accepted Drawdown %
—
of total tank capacity usable
Formula used: V_tank = (Q × 60) ÷ (cycles/hr × acceptance_ratio)
Based on AWWA and pump manufacturer standards. Always consult a licensed plumber for final installation.
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What is Short-Cycling?

Short-cycling happens when your pump turns on and off too rapidly — sometimes hundreds of times per day. Each startup draws 6× the running amperage, burning out motors in months instead of years.

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Why Tank Size Matters

A correctly sized pressure tank stores enough water between pump cycles so the pump runs longer, less often. A tank that's too small (or waterlogged) fails to prevent short-cycling entirely.

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The Draw-Down Formula

Draw-down is the actual usable water in your tank — typically 30% of total capacity. Our calculator works backward from your pump's GPM and pressure settings to give you the exact minimum tank size.

How The Calculation Works

01

Pump GPM → Cycle Time

Your pump's GPM tells us how long each pump cycle lasts. Faster pumps need more draw-down to prevent rapid cycling.

02

Pressure Differential → Acceptance

The difference between cut-in and cut-out PSI, plus the pre-charge air pressure, determines what fraction of the tank actually holds water.

03

Cycles/hr → Min Draw-Down

We calculate the minimum draw-down volume needed to keep your pump under its rated cycles-per-hour limit.

04

Draw-Down → Tank Size

Dividing the required draw-down by the acceptance ratio gives your minimum tank size. We recommend the next standard size up.

Common Questions

Tank size is the total gallons stamped on the side. Draw-down is the actual usable water you can draw before the pump kicks on. For a typical 40-60 PSI system, draw-down is about 30% of tank capacity. A 44-gallon tank holds roughly 13–14 gallons of usable water.
The most common residential settings are 30/50 PSI (low pressure) or 40/60 PSI (standard). 40/60 is recommended for homes with two or more stories or where good shower pressure is important. The exact setting is found on your pressure switch — a gray box near your pressure tank with a label.
Rapid cycling (every 1–10 seconds) almost always means a waterlogged pressure tank — the bladder has failed and no longer holds air. Check by pressing the Schrader valve on top of the tank with the pressure off. If water comes out instead of air, the bladder is ruptured and the tank needs replacement.
Check the nameplate on your pump motor, your original well driller's report, or the pump manufacturer's model number lookup. As a rough rule of thumb: ½ HP pumps typically deliver 5–7 GPM, ¾ HP deliver 7–10 GPM, and 1 HP pumps deliver 10–15 GPM at standard pressures.
In most residential cases, bigger is better. An oversized tank extends pump life, reduces energy use, and provides more buffer during power outages. The only downsides are cost and space. Going 1–2 sizes above the calculated minimum is generally a sound decision.
Always set pre-charge to 2 PSI below your cut-in pressure. If your pressure switch cuts in at 40 PSI, set the tank pre-charge to 38 PSI. Check this with a tire gauge at the Schrader valve on top of the tank with the pump off and system pressure released.