Water Well Pump Size Calculator

Check well pump inputs

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Project preset:

Start from the closest home, deep-well, storage, or irrigation scenario, then edit the measurements.

Unit system:

Switch input labels and exported display units while keeping pump-curve GPM and feet of head visible.

System strategy:

Use storage-fill when the well cannot sustainably produce the desired service flow.

Demand profile:

Choose the household or irrigation demand pattern closest to the pump job.

{{ targetFlowLabel }}: {{ formatFlow(base.targetFlowGpm) }}

Direct systems use peak service demand; storage-fill systems usually set this near sustainable well yield.

Well sustainable yield: {{ formatFlow(base.wellYieldGpm) }}

A well pump should not be selected to outrun the well's sustainable recovery without storage and protection.

Daily water use:

Enter expected gallons or liters per day for the household, livestock, or irrigation plan.

{{ volumeUnit }}/day

Static water level: {{ formatLength(base.staticLevelFt) }}

This is not enough by itself; add drawdown to estimate pumping water level.

Pumping drawdown allowance: {{ formatLength(base.drawdownFt) }}

Pumping water level equals static water level plus this drawdown allowance.

Pump setting depth:

Keep the intake below the expected pumping level with adequate submergence from the pump manufacturer or well contractor.

Desired delivery pressure: {{ formatPressure(base.targetPressurePsi) }}

Use the pressure you need at the tank or service point under demand, commonly 40-60 PSI for homes.

Delivery elevation above wellhead:

Use 0 when the pressure tank or service point is roughly level with the wellhead.

Service pipe length after wellhead:

Measure the line from wellhead to pressure tank, storage tank, or main service point.

Drop/service pipe size:

The head worksheet estimates friction from target flow, total pipe length, material, and this size.

Pipe material:

Smooth plastic has lower friction than older steel or mixed piping.

Head reserve: {{ head_reserve_pct }}%

Reserve covers fixture losses, aging, filter pressure drop, and estimate uncertainty.

Candidate pump rating at this TDH:

Use 0 when you are not comparing a specific pump model yet.

Pressure switch:

This does not change TDH unless you also edit desired delivery pressure above.

Minimum pump run time:

Longer minimum run time requires more usable tank drawdown.

sec

Planned atmospheric storage:

Enter tank storage volume when this well pump fills a cistern or atmospheric tank.

Fitting and valve allowance:

Use exact friction calculations for final design when fittings, filters, or treatment equipment are known.

Wire-to-water efficiency: {{ motor_efficiency_pct }}%

Typical small submersible systems vary widely; use the pump curve if available.

Control and protection note:

Flag whether the design includes low-water or constant-pressure protection.

Worksheet item	Value	How it affects pump selection	Copy
{{ row.item }}	{{ row.value }}	{{ row.note }}

Reference class	Estimated flow at TDH	Fit	Curve note	Copy
{{ row.className }}	{{ row.capacity }}	{{ row.fit }}	{{ row.note }}

Check	Status	Detail	Copy
{{ row.check }}	{{ row.status }}	{{ row.detail }}

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A well pump is selected by the water it must deliver at the resistance the system creates. Depth alone is not enough. A pump that can move plenty of water near the surface may deliver far less once it has to lift from a lowered pumping water level, push through pipe, overcome pressure-tank settings, and keep the highest fixture supplied.

Total dynamic head, usually shortened to TDH, connects the well conditions to the pump curve. It combines the vertical lift from the pumping water level, the pressure wanted at the house, elevation change after the wellhead, pipe friction, fitting losses, and a modest reserve. Pump curves then show how many gallons per minute a specific pump can deliver at that head. Reading a zero-head flow label as the usable house flow is one of the common sizing mistakes.

Well yield sets a separate limit. A pump can be strong enough for the house and still be wrong for the aquifer if it pulls faster than the well recovers. Low-yield wells often need storage, flow limiting, and low-water protection instead of a larger pump. Pressure tank drawdown also matters because a pump that cycles too often can wear out controls and motors even when the flow and head look acceptable.

Well pump setup showing static water level, pump intake, service pipe, pressure tank, and total dynamic head components.

Good sizing therefore has two jobs. First, it estimates the operating point in gallons per minute at feet of head. Second, it checks whether the well, pressure tank, controls, and candidate pump can live with that operating point. Manufacturer pump curves, a recent pump test, local electrical and plumbing rules, and installer judgment should still decide the final model.

The calculator is most useful as a screening worksheet before comparing specific pump curves or discussing a quote with a well contractor. It cannot prove water quality, aquifer stability, casing condition, wire sizing, or code compliance.

How to Use This Tool:

Start from measured well data when you have it, then use the output to compare pump curves at the calculated head.

Choose a Project preset and Unit system. Presets such as Deep residential well, Low-yield well with storage, and Residential irrigation zone load realistic starting values that you can edit.
Set the System strategy. Use Direct to pressure tank when the well pump must satisfy house pressure, or Well pump fills storage tank when a separate booster will handle peak household flow.
Enter the Target pump flow, Well sustainable yield, and Estimated daily water use. If yield is unknown, the Yield Tank Checks table will treat that as missing data rather than as a safe design.
Fill in Static water level, Pumping drawdown allowance, Pump setting depth, Desired delivery pressure, Delivery elevation, pipe length, pipe size, and pipe material. The summary should change to an Operating point with total dynamic head.
Use Head reserve and Fitting allowance as modest planning margins. If the pump setting depth is not below the expected pumping water level, fix that input before reading the pump class results.
Enter a Candidate delivered flow at TDH when a quote or pump curve lists delivered GPM at the calculated head, then compare the Pump Match Ladder and Yield Tank Checks.

Read TDH Worksheet first, then verify the candidate pump against the manufacturer's curve rather than relying on horsepower alone.

Interpreting Results:

Operating point is the main sizing result. It combines target GPM with total dynamic head, so it is the point to find on a real pump curve. A pump that looks large by horsepower can still miss the target if its curve falls below the needed flow at that head.

Yield Tank Checks protect against false confidence. A match in the Pump Match Ladder does not mean the well can sustain that flow. If the check says Exceeds yield, Reduce fill flow, or Add protection, treat the result as a design warning.

TDH Worksheet explains which head component is driving the pump requirement.
Hydraulic horsepower screen is a rough floor, not a motor purchase decision by itself.
Pressure tank drawdown estimates the tank volume needed to reach the selected minimum run time.
Reference Curve Chart uses simplified reference curves, so final selection still belongs on the exact pump curve.

Technical Details:

Residential well pump sizing starts with the pumping water level, not the total drilled depth. Static level is the recovered water level when the pump is off. Drawdown is the additional drop while water is being pumped. Their sum is the lift from water surface to the wellhead during demand.

Pressure is converted to feet of water head because pump curves use head rather than pounds per square inch. At ordinary water-system conditions, 1 PSI is treated as 2.31 feet of head. Pipe friction is estimated with a Hazen-Williams style water-pipe calculation using the target flow, total pipe length, roughness factor, and inside diameter.

Formula Core:

The core calculation adds lift, pressure head, elevation, friction, fittings, and reserve before screening horsepower.

\begin{array}{lcl} PWL & = & static water level + drawdown allowance \\ TDH & = & PWL + (pressure PSI \times 2.31) + elevation head + pipe friction + fitting head + reserve head \\ BHP & = & \frac{GPM \times TDH}{3960 \times efficiency} \end{array}

For the default deep-well profile, 220 ft static level plus 55 ft drawdown gives a 275 ft pumping level. A 50 PSI pressure target adds 115.5 ft of pressure head. With pipe, fittings, elevation, and 12% reserve included, the operating point is about 10 GPM at 469 ft of head, and the hydraulic horsepower screen rounds up to a larger standard motor class.

Water well pump sizing quantities and interpretation
Quantity	How it is used	Common mistake
Pumping water level	Static level plus drawdown allowance becomes the vertical lift component.	Using total well depth or static level alone instead of the pumping level.
Pressure head	Desired delivery pressure is converted from PSI to feet of head.	Forgetting that a 50 PSI target adds more than 100 ft of head.
Well yield	Sustained recovery is compared with pump target and candidate flow.	Assuming a pressure tank burst test proves aquifer recovery.
Pressure tank drawdown	Target flow multiplied by run time estimates usable gallons per cycle.	Confusing total tank shell volume with usable drawdown.

Boundary Checks:

The warning logic treats yield, submergence, tank drawdown, pipe velocity, and candidate pump flow as separate checks because each can fail independently.

Water well pump checks and corrective action
Check	Risk signal	Corrective direction
Well yield	Target flow exceeds sustained yield for a direct-pressure system.	Lower flow, use storage, or add low-water protection.
Submergence	Pump intake is too close to the pumping water level.	Verify pump setting depth and expected drawdown with a pump test.
Pipe velocity	Velocity rises into a high-friction range.	Review pipe diameter, service length, and flow target.
Candidate pump	Delivered GPM at TDH is below target or far above yield.	Read the exact manufacturer curve and controls before buying.

Accuracy Notes:

This is a planning estimate for pump selection discussions. Several field conditions can change the final answer:

Actual pump curves, impeller trim, voltage, wire length, controller settings, and motor efficiency can move the usable flow.
Well yield should come from a sustained pump or recovery test, especially for low-yield wells.
Local plumbing, electrical, pressure relief, sanitary sealing, and permitting requirements may add constraints not represented here.

Worked Examples:

Deep residential well. A 10 GPM target with 220 ft static level, 55 ft drawdown, 50 PSI delivery pressure, 15 ft elevation, 180 ft service pipe, and 12% reserve produces an Operating point near 10 GPM at 469 ft TDH. The Pump Match Ladder shows smaller reference classes falling short while larger classes carry flow headroom, but Yield Tank Checks still flag that an 8 GPM sustained yield is below the direct target.

Low-yield well with storage. A 4 GPM storage-fill profile with 4 GPM yield and a 500 gallon storage tank should be read differently from a direct-pressure house pump. The Operating point sizes the well pump for a controlled fill rate, while a separate booster would handle household peak demand from storage.

Bad input recovery. If Pump setting depth is entered shallower than static level plus drawdown, the summary stays in a check-input state and reports that the pump setting must be below the expected pumping water level. Correct the depth before trusting TDH, tank, or candidate pump rows.

FAQ:

Is pump horsepower the same as pump size?

No. Horsepower is only one screen. The pump must deliver the target GPM at the calculated TDH, and that match comes from the pump curve.

Should I use static water level or total well depth?

Use static water level plus expected pumping drawdown for lift. Total drilled depth is not the same as pumping water level.

What if the well yield is lower than the house target?

The check will warn when target flow outruns sustainable yield. Low-yield designs usually need storage, controlled fill flow, and dry-run protection rather than a larger direct-pressure pump.

Why does the pressure tank result seem larger than expected?

The tank check uses usable drawdown, not total tank shell size. A pressure tank can hold much less usable water than its nameplate volume between cut-in and cut-out pressure.

Glossary:

Total dynamic head: Total pump head after lift, pressure, elevation, friction, fittings, and reserve are included.
Static water level: Depth from the wellhead or grade to the recovered water surface when the pump is off.
Drawdown: Additional water-level drop while pumping at the selected flow.
Well yield: Sustained recovery rate of the well, usually stated in gallons per minute.
Pressure tank drawdown: Usable water delivered between pressure switch cut-in and cut-out.

References:

Group B Public Water Systems - Design, Washington State Department of Health.
Learn About Private Water Wells, U.S. Environmental Protection Agency, October 1, 2025.
Guidelines for Testing Well Water, Centers for Disease Control and Prevention, July 1, 2024.