Well Pump Size Calculator (GPM and Total Dynamic Head)
Estimate the flow rate your household needs and the total dynamic head the pump must work against.
What size well pump do I need?
Minimum pump flow by bathroom count, from the Water Systems Council's 7-minute peak demand table. Add irrigation or livestock flow if it runs at peak.
| Bathrooms | 7-minute peak | Minimum pump flow |
|---|---|---|
| 1 | 45 gal | 7 gpm |
| 1½ | 70 gal | 10 gpm |
| 2 to 2½ | 98 gal | 14 gpm |
| 3 to 4 | 122 gal | 17 gpm |
Worked example
The Water Systems Council's example house has 2 bathrooms (toilet, tub/shower and sink in each), a kitchen sink, disposal, dishwasher, washing machine, laundry sink and 3 hose bibs: 14 fixtures, so 14 gpm. Its 7-minute peak table gives the same answer for a 2-bathroom home: 98 gallons of peak demand and a 14 gpm minimum pump. For head, a 50 psi cut-out is 50 × 2.31 = 115.5 feet. Add the pumping level, elevation rise and friction loss to get the total.
How it works
Size the pump for peak demand, not average use. Total dynamic head (TDH) is the pumping water level, plus the vertical rise to the tank, plus friction loss in the pipe, plus the cut-out pressure converted to feet (1 psi = 2.31 ft). Take friction loss from the pipe maker's friction table for your pipe size, length and flow. Pick a pump whose curve delivers the flow at that head, and make sure the well's tested yield can sustain it.
Questions
How many gpm does a 3-bathroom house need?
The Water Systems Council table lists 17 gpm for 3 to 4 bathrooms (122 gallons over a 7-minute peak).
How do I convert pressure to feet of head?
Multiply psi by 2.31. A 60 psi cut-out adds 138.6 feet.
Does irrigation count?
Yes. The Water Systems Council says to add irrigation, pools, hot tubs and farm use if they run during peak periods.
Sources
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