What Size Well Pump Do I Need? Flow, Then Horsepower
What size well pump you need comes down to two numbers: the flow your household uses at peak, and the head the pump has to push against. Pick the flow from your bathrooms, then read the horsepower off a manufacturer's chart at your depth and pressure.
Step 1: the flow
Goulds' private-residence table sizes the pump to meet a seven-minute morning or evening peak without a supplemental supply:
| Bathrooms | Seven-minute peak | Minimum pump |
|---|---|---|
| 1 | 45 gal | 7 gpm |
| 1½ | 70 gal | 10 gpm |
| 2–2½ | 98 gal | 14 gpm |
| 3–4 | 122 gal | 17 gpm |
Penn State Extension's table, by bedrooms and bathrooms, lands in the same range — 12 gpm for a three-bedroom, two-bath house — and adds a floor: "For most single-family homes, a minimum flow of 6 GPM is suggested from a well or spring." Goulds' rule of thumb for counting fixtures is one gallon per minute each, hose bibs included.
Step 2: the head
The pump has to lift water from the pumping level, raise it to the tank, and reach the switch's cut-out pressure, plus overcome friction. The total dynamic head guide works through it.
Step 3: the horsepower
With the flow and the depth, read the chart. On a 40/60 switch, the smallest model in Goulds' 10GS series that meets each flow:
| Pumping level | 7 gpm | 10 gpm | 14 gpm |
|---|---|---|---|
| 60 ft | ½ hp | ½ hp | ¾ hp |
| 100 ft | ¾ hp | ¾ hp | 1 hp |
| 200 ft | 1 hp | 1 hp | 1½ hp |
| 300 ft | 1½ hp | 1½ hp | 2 hp |
| 380 ft | 1½ hp | 2 hp | 3 hp |
The 17 gpm demand of a three or four-bathroom house is above the 10GS series' recommended 3 to 16 gpm range, so it needs a higher-flow series. Each depth has a full table on well pump size by depth.
Step 4: check the well and the tank
A pump can only deliver what the well yields. New York's health department suggests "a minimum long-term sustainable yield of 5 gpm or more" for a home; a well below that needs storage. And every pump needs a pressure tank sized to give it a one-minute run: a 14 gpm pump on 40/60 needs at least 54 gallons of tank — see pressure tank size.
Flow from your bathrooms, horsepower from your depth: that answers what size well pump you need. The calculator does both with your numbers.
Sources
- Goulds Water Technology (Xylem), Technical Manual TTECHWP R7 — private-residence peak demand and the one-gallon-per-fixture rule.
- Penn State Extension, Water System Planning: Estimating Water Needs.
- New York State Department of Health, Individual Water Supply Wells – Fact Sheet #2.
- Goulds 10GS selection chart (brochure B5-25GS). See the methodology.
Questions
How many gpm does a house need?
Goulds' peak-demand table gives 7 gpm for one bathroom, 10 for one and a half, 14 for two to two and a half, and 17 for three or four. Penn State Extension suggests at least 6 gpm for most single-family homes.
What horsepower well pump for a 200 ft well?
From Goulds' 10GS chart on a 40/60 switch, with water 200 feet down, a 1 hp pump (10GS10) meets 7 or 10 gpm and a 1½ hp pump (10GS15) meets 14 gpm, before adding rise and pipe friction.
Does the well have to produce as much as the pump?
Over the long run, yes. New York's health department suggests a sustainable yield of at least 5 gpm for a home; the pressure tank and the well's own storage cover short peaks.