What Size Well Pump Do I Need? Calculator and Sizing Guide
Buy a well pump that is too small and your showers turn weak the moment someone runs the washer. Buy one that is too big and it short cycles, overworks a low yield well and burns out early.
The right size comes down to two numbers: how many gallons per minute (GPM) your home uses at peak, and how many feet of head the pump has to push against. The calculator below works out both, then estimates the horsepower and pump type.
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| Home | Peak demand | Common pump size |
|---|---|---|
| 1 bathroom | About 7 GPM | 1/2 to 3/4 HP, 7 to 10 GPM |
| 2 bathrooms | About 10 to 12 GPM | 3/4 to 1 HP, 10 to 12 GPM |
| 3 to 4 bathrooms | About 14 to 17 GPM | 1 to 1.5 HP, 15 to 18 GPM |
| Home plus irrigation | 17 GPM or more | 1.5 to 2 HP or larger, sized to the irrigation zones |
Horsepower depends on depth. A deep well needs more HP for the same flow, so use the calculator for your numbers.
Well Pump Size Calculator
Enter your fixtures and your well details. Results update as you type.
Step 1: count the water fixtures in your home.
Step 2: describe your well and plumbing.
Pump type:
The pump curve must still reach at least 209 ft at low flow so it can hit your cut-out pressure.
Shop pumps in this size on AmazonEstimate only. It uses the Water Systems Council fixture method (1 GPM per fixture), average switch pressure x 2.31 ft, the Hazen Williams formula for plastic pipe plus 10% for fittings, and hydraulic power at 55% to 65% of motor nameplate horsepower. Always confirm on the maker’s pump curve.
Step 1: Work Out Your Peak Flow (GPM)
The Water Systems Council method is simple: count every fixture that uses water and allow 1 GPM per fixture. A typical bathroom has three (toilet, sink, shower or tub), a kitchen has two (sink and dishwasher), and each outdoor hose bib counts as one.
A two bathroom home with a kitchen, a washer, two hose bibs and a softener comes to about 12 fixtures, so it needs about 12 GPM. If you irrigate, size for whichever is bigger: the house or the largest irrigation zone you run.
Step 2: Work Out Total Dynamic Head (TDH)
Total dynamic head is the total resistance the pump works against, measured in feet of water. It has four parts:
- Pumping water level. The depth to the water while the pump is running, not the static level. Drawdown can add tens of feet in a slow well.
- Vertical lift. The height from the well head up to the pressure tank. Subtract it if the house sits below the well.
- Pressure. Every 1 psi equals 2.31 feet of head. A 40/60 switch averages 50 psi, which is about 116 feet.
- Friction loss. Water rubbing against pipe and fittings. It grows fast with flow and shrinks fast with bigger pipe.
For example, a pumping level of 60 feet, 10 feet of lift, 116 feet of pressure and 4 feet of friction adds up to about 190 feet of TDH.
Well water level meter (sounder)
The pumping level is the number most people guess wrong. A tape style water level meter reads the real depth in a few minutes, before and after the pump runs.
- Graduated tape with probe and buzzer or light
- Measures static and pumping levels
- Check the well cap has an access port first
Turns the biggest unknown in pump sizing into a real number.
Some wells need the cap or seal opened to fit the probe.
See our guide to the best water level meters and well sounders for options.
Step 3: Match Flow and Head to Horsepower
Pump makers sell pumps by GPM rating and horsepower, and each model has a curve showing the flow it delivers at each head. Pick the curve that gives your GPM at your TDH, then check that it can still reach your cut-out pressure at low flow.
The table below shows rough horsepower for a typical 10 to 12 GPM submersible at different heads. Treat it as a starting point, then confirm on the curve.
| Total dynamic head | Typical HP at about 10 GPM |
|---|---|
| Up to about 150 ft | 1/2 to 3/4 HP |
| 150 to 250 ft | 3/4 to 1 HP |
| 250 to 350 ft | 1 to 1.5 HP |
| 350 to 450 ft | 1.5 to 2 HP |
| Over 450 ft | 2 HP and up, often 3 phase or a constant pressure drive |
Based on hydraulic horsepower (GPM x feet of head / 3960) at 55% to 65% of motor nameplate horsepower, rounded to standard motor sizes.
Step 4: Choose the Pump Type
| Pumping water level | Best pump type | Why |
|---|---|---|
| Up to about 25 ft | Shallow well jet pump | Suction lift is limited by air pressure. Most jet pumps stop pulling well past about 25 feet. |
| About 25 to 90 ft | Submersible, or a convertible deep well jet | A deep well jet uses an ejector in the well. It works, but a submersible is usually quieter and more efficient. |
| Over about 90 ft | Submersible well pump | It pushes water up instead of pulling, so depth is limited only by the pump curve. |
| Any depth, steady pressure wanted | Constant pressure system | A variable speed drive matches pump speed to demand, so pressure stays even and the tank can be smaller. |
When Your Well Cannot Keep Up
If your well yields less than your peak demand, a bigger pump will only drain it faster and risk running dry. Size the pump to the well instead, a little below its yield.
Then cover peak demand with stored water: a storage tank filled slowly by the well pump and a booster pump that feeds the house. A dry run or pump protection device is also worth fitting, as covered in well pump protection devices.
Do Not Forget the Pressure Tank
Pump size and tank size go together. A larger pump needs more drawdown so it runs at least a minute each cycle, or it will short cycle. Once you know your GPM, use our pressure tank sizing calculator to pick the matching tank.
If your pump already turns on and off every few seconds, read well pump short cycling before you replace anything.
Common Well Pump Sizing Mistakes
- Using the static water level. Always size to the pumping level, which is lower once the pump runs.
- Ignoring the pressure switch. Moving from 30/50 to 50/70 psi adds about 46 feet of head.
- Oversizing for a weak well. More GPM than the well can supply pumps it dry.
- Keeping old small pipe. Undersized pipe can add 20 feet or more of friction at high flow.
- Matching the old pump blindly. If the old one was wrong, a copy will be wrong too.
Already shopping because the old pump is failing? Check signs your well pump is going bad and estimate remaining life with the well pump lifespan calculator.
Frequently Asked Questions
What size well pump do I need for a 2 bathroom house?
Most 2 bathroom homes need about 10 to 12 GPM. At a typical total dynamic head of 150 to 250 feet that usually means a 3/4 to 1 HP submersible, but confirm with your pumping level and pressure setting.
How many GPM does a house need from a well?
Allow 1 GPM per water fixture. Most homes need 7 to 17 GPM depending on the number of bathrooms, plus extra if you irrigate.
Is a 1 HP well pump enough?
A 1 HP submersible typically delivers about 10 GPM at around 200 to 250 feet of head. That suits many 2 to 3 bathroom homes with moderate well depth.
Can a well pump be too big?
Yes. An oversized pump short cycles, wastes power and can pump a low yield well dry. Size it to your peak demand and never above what the well can supply.
How do I calculate total dynamic head for a well pump?
Add the pumping water level, the vertical lift to the pressure tank, the average pressure switch setting times 2.31 and the pipe friction loss. The total, in feet, is your TDH.
Sources: Water Systems Council (fixture count method); National Driller, Sizing a Residential Water System; RC Worst, Submersible Well Pump Sizing (TDH components); Franklin Electric (pump curves and minimum run time).
