Well Pump Size Calculator
Sizing a submersible well pump means matching two things: GPM demand at peak use and total dynamic head (TDH). This well pump size calculator covers both. It answers what size well pump do i need for my house by totaling pumping water level, elevation rise, friction loss, and target pressure, then maps the result to the closest standard horsepower on the Goulds and Grundfos sizing charts.
What Size Well Pump Do I Need for My House?
The answer depends on three things: how many fixtures run at once (GPM), how deep the water is (pumping level), and what pressure you want at the fixtures.
- 1-2 bath home: 6-7 GPM, typically 1/2 HP if well is under 100 ft
- 3 bath home (typical): 8 GPM, 3/4 to 1 HP for wells 100-250 ft
- 4+ bath home with irrigation: 10-15 GPM, 1.5-2 HP for deep wells
Submersible Well Pump Sizing Chart
| Home Size | Peak GPM | Well Depth | TDH | Recommended HP |
|---|---|---|---|---|
| 1-2 bath | 6 GPM | 100 ft | 250 ft | 1/2 HP |
| 3 bath | 8 GPM | 200 ft | 350 ft | 1 HP |
| 3 bath + irrigation | 10 GPM | 200 ft | 400 ft | 1.5 HP |
| 4-5 bath | 12 GPM | 250 ft | 450 ft | 2 HP |
| 5+ bath deep | 15 GPM | 400 ft | 600 ft | 3 HP |
This submersible well pump sizing chart is a starting point. Use the calculator above with your actual numbers from the well log.
Goulds Well Pump Sizing Chart
The Goulds well pump sizing chart (GS series) is the industry reference. Goulds GS models are rated at specific GPM-vs-TDH points on their pump curves. The formula used by the Goulds well pump sizing chart:
HP = GPM x TDH / (3960 x efficiency)
Efficiency for submersibles is about 60%. This calculator applies the same formula and rounds up to the nearest standard HP size (1/2, 3/4, 1, 1.5, 2, 3, 5 HP).
Calculating Total Dynamic Head
- Pumping water level (lift): depth to water during pumping, from the well log
- Elevation rise: vertical distance from the wellhead up to the pressure tank
- Friction loss: about 3.5 ft per 100 ft of 1-inch PVC at 10 GPM
- Pressure head: 50 psi = 115 ft (2.31 ft per psi). 40/60 psi switch = 50 psi average.
Add these four numbers for your TDH.
Well Pump Size Calculator PDF
Pump manufacturers publish a well pump size calculator pdf with worksheet forms: Goulds, Grundfos, Franklin Electric, and Sta-Rite each have one. They all use the same underlying math as this calculator. The advantage of using this tool over a pump size calculator pdf is that it updates in real time as you change inputs.
Avoid Oversizing
A bigger pump is not better. Oversizing causes:
- Short-cycling that burns out the motor and pressure switch
- Higher electric bills (larger motor, same output)
- Pressure spikes that stress fittings
- Reduced well recovery time
Size to peak demand + 20% safety margin, not 3x.
Common Well Pump Brands and Sizes
- Goulds GS series: 1/2 to 5 HP, 5-25 GPM range
- Grundfos SQ series: 1/2 to 3 HP, 5-30 GPM
- Franklin Electric: motors for most pump brands, 1/3 to 7.5 HP
- Sta-Rite / Pentair: 1/2 to 5 HP residential