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 private well pump has to satisfy the water system's peak demand without outrunning the well. Those two limits are not the same. The pump may move plenty of water in a shallow test, then deliver much less once it is lifting from a deep pumping water level, pushing through a long service line, and building pressure at the tank or fixtures.

Pump size is often discussed in gallons per minute and horsepower, but the useful sizing point is gallons per minute at total dynamic head. Total dynamic head, or TDH, is the pump's working load expressed as feet of water head. It includes lift from the pumping water level, desired pressure converted into head, elevation change, pipe friction, fittings, and a planning reserve. A 10 GPM label is incomplete because the same pump may deliver 10 GPM at one head and much less at another.

Well yield deserves equal attention. Yield is the sustained recovery rate measured during a pump or recovery test, not the short burst a pressure tank can provide. A low-yield well can still serve a home when storage, flow limiting, and dry-run protection are designed around it. Installing a larger pump to chase peak household demand can make the system worse if it pulls the water level down to the pump intake.

Pumping water level: The water depth while the pump is running, usually static water level plus drawdown.
Pressure head: The desired delivery pressure expressed as feet of head, commonly using 2.31 ft per PSI.
Pump curve: The manufacturer chart that shows delivered flow at different heads for a specific pump model.

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

Pressure tanks and controls do not remove the need for correct pump selection. The tank stores usable drawdown between cut-out and cut-in pressure so the pump does not start for every small faucet draw. The controller, pressure switch, low-water protection, and storage tank plan all affect whether a pump that looks acceptable on a curve will run without short cycling or overpumping the well.

A sizing estimate is a planning aid, not a purchase approval. The final pump should be checked against the exact manufacturer curve, sustained well test data, wire and voltage limits, pressure relief requirements, local code, and the installer or well contractor's field judgment.

How to Use This Tool:

Use measured well and pipe data when available. Presets are useful starting points, but the operating point becomes meaningful only when the numbers resemble the actual installation.

Choose a Project preset and Unit system. The preset fills a realistic starting profile, and the unit setting changes the visible input labels while still keeping pump-curve values in GPM and feet of head.
Set System strategy. Select Direct to pressure tank when the well pump must supply service pressure directly, or Well pump fills storage tank when a storage tank and booster pump will handle household peaks.
Enter Target service flow or Target well-pump fill flow, Well sustainable yield, and Daily water use. The yield and daily-use values drive the Yield Tank Checks warnings.
Fill in Static water level, Pumping drawdown allowance, Pump setting depth, Desired delivery pressure, Delivery elevation above wellhead, service pipe length, pipe size, and pipe material. When these inputs are valid, the summary changes to an Operating point.
Use Head reserve and Fitting and valve allowance for modest planning margin. If the page reports that the pump setting must be below the expected pumping water level, correct the depth before using the TDH, pump ladder, or charts.
Open Advanced for Pressure switch, Minimum pump run time, storage volume, efficiency, and control protection notes. These settings affect tank sizing, horsepower screening, and warning text.
Enter Candidate pump rating at this TDH when a quote or pump curve gives delivered GPM at the calculated head. Then compare TDH Worksheet, Pump Match Ladder, Reference Curve Chart, and Yield Tank Checks.

If an input is missing or out of range, the error box names the field that needs attention and the result tabs stay unavailable until the sizing inputs are usable again.

Interpreting Results:

Operating point is the first result to trust. It combines target flow and TDH, so it is the point to locate on a pump curve. Horsepower alone can mislead because two pumps with the same motor size can have different impeller stacks, efficiency ranges, and flow at high head.

Pump Match Ladder is a screening comparison, not a substitute for a model-specific curve. A Curve match or Yield caution means the reference class clears the simplified curve screen; it does not prove the chosen pump will operate in its preferred efficiency range.

TDH Worksheet shows whether lift, pressure, elevation, pipe friction, fittings, or reserve is driving the head requirement.
Yield Tank Checks should override a tempting pump match when the target flow exceeds sustainable well yield.
Pressure tank drawdown estimates usable gallons for the selected run time; it is not the same as total tank shell volume.
Candidate pump curve is most useful when the entered candidate flow comes from the exact pump curve at the calculated TDH.

Technical Details:

Well-pump sizing math normally keeps pump curves in gallons per minute and feet of head because most residential pump curves are published in those units. Metric measurements can be converted into the same working units, but the operating point still has to land on a curve as flow at head.

Lift head is based on the pumping water level, not the total drilled depth or the physical pump setting. Once the casing is full of water above the pump, the pump is working against the water level under load. Pump setting depth still matters for submergence, cooling, and intake protection, so a shallow setting can fail the installation check even when the TDH arithmetic is otherwise valid.

Formula Core:

The main sizing relationship adds the head components, applies reserve, and then estimates a brake horsepower floor from flow, TDH, and the selected efficiency.

\begin{array}{lcl} PWL & = & static water level + drawdown allowance \\ H_{p} & = & delivery pressure in PSI \times 2.31 \\ H_{f} & = & \frac{4.52 \times L \times Q^{1.85}}{C^{1.85} \times d^{4.87}} \\ TDH & = & (PWL + H_{p} + elevation + H_{f} + fittings) \times (1 + reserve) \\ BHP & = & \frac{Q \times TDH}{3960 \times efficiency} \end{array}

Formula symbols for water well pump sizing
Symbol	Meaning	Tool input or source
PWL	Pumping water level in feet	Static water level plus Pumping drawdown allowance
Q	Target flow in GPM	Target service flow or Target well-pump fill flow
L	Total pipe length in feet	Pumping water level plus Service pipe length after wellhead
C	Hazen-Williams roughness factor	Pipe material, using 150 for PVC, 140 for poly, or 120 for older steel
d	Inside pipe diameter in inches	Drop/service pipe size

For the default deep residential well, the pumping water level is 275 ft, pressure head from 50 PSI is 115.5 ft, and the calculated operating point is about 10 GPM at 469 ft TDH after pipe, fittings, elevation, and 12% reserve are included. With 55% wire-to-water efficiency, the horsepower screen is about 2.15 HP and rounds to a 3 HP motor floor.

Rule Checks:

Water well pump sizing rule checks
Check	Main rule	Result meaning
Sustainable well yield	Target flow is compared with measured yield, with a comfortable margin below 85% of yield.	Warnings appear when the design is tight, exceeds yield, or needs a lower storage-fill rate.
Pipe velocity	Velocity above 8 ft/s is a caution and above 10 ft/s is a high-velocity warning.	High velocity can increase friction, noise, and pressure drop in long runs.
Pump setting depth	The pump intake must be below the expected pumping water level; less than 20 ft of submergence is flagged.	Submergence warnings should be checked against the pump maker's intake and cooling requirements.
Candidate pump curve	Entered candidate flow must be at least 95% of target flow at the calculated TDH.	A pump can be short, oversized, yield-limited, or acceptably close depending on flow and well yield.
Pressure tank drawdown	Target flow times minimum run time estimates usable drawdown; pressure settings estimate the total tank volume needed.	Constant-pressure controllers are marked as controller-specific because VFD tank sizing follows the controller maker's rules.

Reference pump classes use simplified curves with no-head flow, shutoff head, and a curved falloff toward zero flow. They are meant to show the relationship between head and flow before reviewing exact pump models, not to replace a manufacturer's published performance data.

Accuracy Notes:

This estimate is useful for screening a pump quote or planning a contractor discussion, but several field details can move the final selection:

Use a sustained pump test or recovery test for well yield and drawdown whenever possible.
Confirm the exact pump curve, efficiency band, motor, voltage, wire length, controls, and pressure relief requirements before purchase.
Water quality, well construction, casing condition, sanitary sealing, and local permitting are outside this sizing calculation.
Private well water should still be tested and maintained according to local health guidance; pump sizing does not prove water safety.

Worked Examples:

Deep residential well. With Target service flow at 10 GPM, Static water level at 220 ft, Pumping drawdown allowance at 55 ft, 50 PSI delivery pressure, 180 ft of service pipe, and 12% head reserve, the Operating point is about 10 GPM at 469 ft TDH. The Pump Match Ladder shows smaller reference classes short, but the higher classes carry Yield caution because the entered well yield is only 8 GPM.

Low-yield well with storage. A storage-fill setup at 4 GPM yield and 4 GPM target fill flow gives an Operating point near 4 GPM at 432 ft TDH for the preset values. The Yield Tank Checks read this as a tight yield condition, so the well pump should be controlled as a fill pump and a separate booster should handle peak house pressure from storage.

Shallow pump setting entry. If Pump setting depth is entered shallower than Static water level plus Pumping drawdown allowance, the summary changes to Check inputs and reports that the pump setting must be below the expected pumping water level. Correct the depth before relying on TDH Worksheet, Reference Curve Chart, or Yield Tank Checks.

FAQ:

Should I size by total well depth?

No. The calculator uses static water level plus pumping drawdown for lift. Total drilled depth matters for well construction and pump placement, but it is not the same as pumping water level.

Why does 50 PSI add so much head?

The pressure input is converted to feet of head with PSI times 2.31, so 50 PSI adds about 115.5 ft before elevation, friction, fittings, and reserve are added.

What if the well yield is lower than target flow?

The yield check warns when direct service flow exceeds sustainable yield. Consider a lower pump flow, storage-fill strategy, low-water protection, or a contractor review instead of simply choosing a larger pump.

Why is the tank result not the same as tank size?

The tank check estimates usable drawdown between pressure switch settings. A tank's total shell volume is much larger than the water it can deliver between cut-out and cut-in pressure.

Can the reference curve chart choose the final pump?

No. The chart uses simplified reference classes. Use the calculated Operating point on the exact manufacturer pump curve, then verify controls, efficiency, submergence, and well yield.

Glossary:

Total dynamic head: The total pump load after lift, pressure head, elevation, pipe friction, fittings, and reserve are included.
Pumping water level: The water level in the well while pumping at the selected flow.
Drawdown: The drop from static water level to pumping water level during pumping.
Well yield: The sustained rate the well can produce without pulling the water level too low.
Pressure tank drawdown: The usable water volume delivered between pump shutoff and restart pressure.
Pump curve: A manufacturer performance chart showing flow against head for a specific pump.

References:

Irrigation Water Pumps, North Dakota State University Extension.
Group B Water System Design Guidelines, Washington State Department of Health, September 2018.
Well Owner's Handbook: A Consumer's Guide to Water Wells in Minnesota, Minnesota 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.