What Size Well Pump Do I Need? — Well Pump Size Calculator
A well pump that's too small can't keep up when two showers and the washing machine run at once — and one that's too big short-cycles and can run a low-yield well dry. This free well pump size calculator estimates your home's fixture count, peak GPM demand, and total dynamic head, then recommends the right pump horsepower (HP) and pump type — instantly, right in your browser.
Enter your numbers
Not sure of your peak demand? Use the fixture estimate below as a starting point — the table shows both.
Your results
How to use this calculator
Enter the number of bedrooms in your home. A standard sizing rule is that fixture count ≈ bedrooms + 1 (so a 3-bedroom home has about 4 fixtures: bathrooms, kitchen, laundry, and outdoor spigot). Then enter your well depth in feet — the depth where the pump sits, or the drilled depth if you don't know the set depth.
Enter your peak water demand in GPM — the most water your household can draw at once. If you don't know it, the fixture-based estimate in the results table is a good starting point: fixtures × 2 GPM. The calculator instantly recommends a pump size in horsepower, tells you whether a submersible or jet pump fits your well, and shows your estimated total dynamic head.
How it works
GPM demand. The standard rule of thumb for residential sizing is: fixture count = bedrooms + 1, with each fixture averaging about 2 GPM. A 3-bedroom home therefore has about 4 fixtures and a theoretical peak of 8 GPM — but because fixtures rarely all run at once, the usual design value is 7 GPM for 3–4 bedroom homes. The standard bands are: 1–2 bedrooms ≈ 5 GPM, 3–4 bedrooms ≈ 7–10 GPM, and 5+ bedrooms ≈ 12+ GPM. If you enter your own peak demand, it takes priority over the estimate.
Total dynamic head (TDH). Head is the total lift the pump must overcome: the vertical well depth plus the pressure in the tank. A typical residential 40–60 psi pressure switch adds about 115 ft of head, so TDH ≈ well depth + 115 ft. A deeper well means more head, and head is the main reason deep wells need bigger pumps — a 120 ft well works out to about 235 ft of total head.
HP selection. The recommendation picks the smallest pump whose GPM band and depth band both cover your demand and TDH: 1/3 HP handles up to about 5 GPM in wells to about 80 ft; 1/2 HP handles up to about 10 GPM in wells to about 150 ft; 3/4 HP handles up to about 12 GPM in wells to about 250 ft; 1 HP and up for larger demand or deeper wells. As a quick rule: 1–2 bed ≈ 1/3–1/2 HP, 3–4 bed ≈ 1/2–3/4 HP, 5+ bed ≈ 1 HP or more, and wells deeper than 150 ft often need 3/4–1 HP even with moderate demand, because the pump must lift water further. All results are estimates — real pump performance varies by model and piping, and this does not replace a well professional's sizing for your specific well.
Frequently asked questions
What size well pump do I need for a 3-bedroom house?
A 3-bedroom home typically has a peak demand of about 7 GPM. For a well under 150 ft deep, a 1/2 HP submersible pump covers that demand. If your well is deeper than 150 ft, step up to a 3/4 HP pump because the extra lift (total dynamic head) raises the workload. Enter your actual well depth above for a tailored estimate.
How do I figure out my peak GPM demand?
A common rule of thumb is: fixture count ≈ number of bedrooms + 1, at an average of 2 GPM per fixture running. A 3-bedroom home therefore has about 4 fixtures and a theoretical peak of 8 GPM, but fixtures rarely all run at once, so a peak demand of 7 GPM is the usual design value. If you know your actual peak demand, enter it directly — it overrides the estimate.
What HP well pump do I need?
As a starting rule: 1–2 bedroom homes need about 5 GPM and a 1/3–1/2 HP pump; 3–4 bedroom homes need about 7–10 GPM and a 1/2–3/4 HP pump; 5+ bedroom homes need about 12+ GPM and a 1 HP or larger pump. Well depth shifts these bands: wells deeper than 150 ft usually need 3/4–1 HP even for moderate demand, because the pump must lift water further.
Should I get a jet pump or a submersible pump?
It depends on depth. Shallow wells of 25 ft or less can use a jet pump mounted above ground. Wells deeper than about 110 ft need a submersible pump — jet pumps with a deep-well ejector top out around 110 ft. For most residential wells (100+ ft), a submersible is the standard choice: it sits in the water, runs quietly, and is more efficient.
Can I use a bigger well pump than I need?
Only one size up, and only when your demand sits near the top of a band. A badly oversized pump cycles on and off rapidly, wastes energy, and can pump a low-yield well dry faster than it recovers, which risks running the pump without water. Size to your demand and depth — bigger is not automatically better.