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Technical Reference

Well Pump Sizing Guide

Selecting the wrong pump size is one of the most common and expensive well system mistakes. An oversized pump burns out quickly. An undersized pump cannot meet demand. Here is how to get it right.

Typical Residential
1/2 to 1 HP
Deep Well (300+ ft)
1 to 1.5 HP
Irrigation System
1.5 to 3 HP
Pressure Setting
40/60 PSI standard
How to Size a Submersible Well Pump
Pump sizing requires knowing three things: (1) required GPM at the house, (2) total dynamic head (TDH) — how hard the pump has to push water, and (3) well yield to avoid overpumping. TDH = pumping water level depth + vertical rise to pressure tank + friction losses in pipe. A pump must deliver the required GPM at the calculated TDH — this is shown on the pump performance curve.
Total Dynamic Head (TDH) Calculation
Example: Well depth 200 feet, static water level 80 feet, pumping water level 150 feet (drops 70 feet when pumping). Pressure tank is in basement 8 feet below grade. TDH = 150 + 8 (rise to basement) + 50 feet (equivalent friction in 300 ft of 1-inch pipe at 5 GPM) + 92 feet (pressure tank at 40 PSI) = approximately 300 feet TDH. Look up a pump that delivers 5 GPM at 300 feet TDH.
HP Guidelines by Depth
1/2 HP pump: adequate for wells under 150 feet, 5–7 GPM. 3/4 HP: wells 150–250 feet, 7–10 GPM. 1 HP: wells 250–350 feet, 10+ GPM. 1.5 HP: wells 350–500 feet or irrigation use. 2+ HP: deep wells over 500 feet or high-demand commercial/irrigation. Always verify with the pump performance curve rather than HP alone — HP is a rough guide.
Pressure Tank Sizing
The pressure tank stores water between pump cycles. Too small a tank = pump short cycling = premature pump failure. Rule of thumb: pressure tank drawdown capacity should be at least 1 gallon per GPM of pump rate. For a 5 GPM pump, minimum 5 gallons drawdown — a 20-gallon tank. Better: 10 gallons drawdown per GPM of pump rate. A 42-gallon tank for a 5 GPM pump is a good standard.
Common Pump Sizing Mistakes
(1) Pump rated higher than well yield — draws well down and runs pump dry. (2) Pressure tank too small — causes short cycling and premature pump failure. (3) Ignoring pipe friction — using undersized pipe creates head loss that reduces effective pump output. (4) Not accounting for elevation — a house at higher elevation than the well requires more TDH.
Common Questions
A 3-bedroom house typically needs 5–7 GPM at the house. For a well 150–250 feet deep, a 3/4 HP to 1 HP submersible pump is typical. Have a well contractor calculate the Total Dynamic Head for your specific well depth and pipe configuration before selecting a pump.
Quality submersible well pumps last 10–20 years. Shorter life (5–8 years) usually results from pump short cycling (too-small pressure tank), running dry due to overpumping, or poor water quality with sand or sediment. A properly sized pump with an adequate pressure tank regularly lasts 15–20 years.
The standard residential pressure setting is 40/60 PSI — the pump starts at 40 PSI and shuts off at 60 PSI. Some homes prefer 50/70 PSI for better shower pressure. Higher settings reduce pump life slightly. Pressure setting is adjusted at the pressure switch on the pressure tank.
Short cycling (pump turns on and off rapidly) is almost always caused by a waterlogged pressure tank — one that has lost its air charge and cannot store adequate water. The fix is to check and restore the tank pre-charge air pressure (should be 2 PSI below the pump cut-in pressure) or replace the tank if the bladder has failed.
Related Topics
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Water Well Yield — GPM Requirements & Calculation
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Water Well Casing Size Guide
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Well Water Treatment Guide
Important: Well drilling costs, depths, and regulations vary significantly within each state. This page provides general reference information only. Always get quotes from multiple licensed well contractors in your area and verify current state regulations before proceeding.