Well Pump Sizing Guide: How to Choose the Right Pump
📋 In This Guide
Sizing a well pump correctly is the foundation of a reliable water system. The pump needs to deliver enough water at enough pressure for your household's peak demand — but not so much that it exceeds your well's yield. This guide walks you through the calculation step by step, with the actual formulas and tables you need.
If math isn't your thing, that's OK — the quick-reference tables below will get you close for most residential situations. But if you want to understand why your well pro recommends a specific pump, or if you want to verify a quote, the full calculation is here. For our detailed guide on choosing between pump brands and HP ratings, see our HP sizing guide and pump sizing guide.
Key Sizing Factors
What You Need to Know
- Well depth: Total depth of well
- Static water level: Water level at rest
- Pumping level: Water level when pumping
- Well yield: How much the well produces (GPM)
- Required flow: How much you need (GPM)
- Desired pressure: Usually 40-60 PSI
- Pipe size and distance: Affects friction loss
Why Proper Sizing Matters
- Undersized: Not enough water or pressure
- Oversized: Wastes energy, rapid cycling
- Correct: Efficient operation, long life
Pump Types by Application
| Depth | Pump Type |
|---|---|
| 0-25 feet | Jet pump (shallow well) |
| 25-100 feet | Deep well jet pump or submersible |
| 100+ feet | Submersible pump |
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Flow Rate (GPM)
Household Demand
| Fixture | Flow Rate |
|---|---|
| Shower | 2-3 GPM |
| Bathroom faucet | 1-2 GPM |
| Kitchen faucet | 2-3 GPM |
| Dishwasher | 2-3 GPM |
| Washing machine | 3-5 GPM |
| Toilet | 3 GPM (during fill) |
| Garden hose | 3-5 GPM |
Calculating Peak Demand
Assume multiple fixtures running at once:
- Small home (1-2 bath): 6-10 GPM
- Medium home (2-3 bath): 10-15 GPM
- Large home (3+ bath): 15-20 GPM
- With irrigation: Add irrigation demand
Well Yield Limitation
Pump can't exceed well yield. If well produces 5 GPM, size pump for that maximum. Use storage tank if demand exceeds yield.
Total Dynamic Head (TDH)
The Formula
TDH = Pumping Level + Pressure Head + Friction Loss
Component Details
Pumping Level
- Depth to water when pump is running
- Usually 10-50 feet below static level
- Depends on well yield and pumping rate
Pressure Head
- Convert PSI to feet: PSI × 2.31 = feet
- 50 PSI = 115.5 feet of head
- 60 PSI = 138.6 feet of head
Friction Loss
- Depends on pipe size and length
- Bigger pipe = less friction
- Fittings add friction
- Use friction loss charts
Example Calculation
- Pumping level: 250 feet
- Pressure desired: 50 PSI = 115 feet
- Friction loss: 25 feet
- TDH = 250 + 115 + 25 = 390 feet
Select pump that delivers required GPM at 390 feet TDH.
Horsepower Guide
General Guidelines
| Depth | Typical HP | GPM Range |
|---|---|---|
| Under 100 ft | 1/2 - 3/4 HP | 10-15 GPM |
| 100-200 ft | 3/4 - 1 HP | 8-12 GPM |
| 200-400 ft | 1 - 1.5 HP | 8-12 GPM |
| 400-600 ft | 1.5 - 2 HP | 6-10 GPM |
| 600-800 ft | 2 - 3 HP | 5-8 GPM |
These are general guidelines. Actual sizing requires calculating TDH for your specific conditions.
Higher HP Needed If
- Long horizontal pipe runs
- Higher pressure needed (60+ PSI)
- Larger flow rate required
- Small pipe diameter
Read Pump Curves
Every pump has a performance curve showing GPM vs. head. Select pump where your operating point falls in the efficient range (middle of curve).
Sizing Examples
Example 1: Typical San Diego Home
- Well depth: 400 feet
- Static level: 150 feet
- Pumping level: 200 feet
- Need: 10 GPM at 50 PSI
Calculation:
- Pumping level: 200 ft
- Pressure head: 50 × 2.31 = 115 ft
- Friction (estimate): 20 ft
- TDH: 200 + 115 + 20 = 335 ft
Result: 1.5 HP submersible pump rated for 10 GPM at 335+ ft head.
Example 2: Deep Mountain Well
- Well depth: 700 feet
- Pumping level: 400 feet
- Need: 8 GPM at 50 PSI
Calculation:
- Pumping level: 400 ft
- Pressure head: 115 ft
- Friction: 30 ft
- TDH: 400 + 115 + 30 = 545 ft
Result: 2-3 HP submersible pump rated for 8 GPM at 545+ ft head.
Frequently Asked Questions
What size well pump do I need?
Calculate your Total Dynamic Head (TDH) and required flow rate (GPM), then match those numbers to a pump performance curve. For most residential wells in Southern California: 3/4 HP for wells under 200 feet, 1 HP for 200-300 feet, 1.5 HP for 300-400 feet, and 2+ HP for 400+ feet. These are rough guides — actual sizing requires your specific well data (pumping level, required PSI, pipe diameter, and distance from well to house).
How do I calculate Total Dynamic Head (TDH)?
TDH = Pumping water level (feet) + Pressure requirement (PSI × 2.31 to convert to feet) + Friction losses (from pipe length and diameter). For example: 200-foot pumping level + 50 PSI (= 115.5 feet) + 20 feet friction = 335.5 feet TDH. Select a pump that delivers your required GPM at this TDH — check the manufacturer's performance curve chart.
Can I oversize my well pump?
You can, but you shouldn't. An oversized pump draws water faster than the well recovers (risking dry-run damage), short cycles against the pressure tank (killing pump lifespan), and wastes electricity. The best pump is one matched precisely to your well's yield and your household's demand — not the biggest one that fits.
What if my well doesn't produce enough water?
If your well yields less than your peak demand (common with wells under 5 GPM), do not install a bigger pump — it'll just pump the well dry faster. Instead, size the pump to match the well's sustainable yield and install a storage tank system. The pump slowly fills the tank during off-peak hours, and a booster pump delivers water from the tank to the house at full pressure and flow rate during peak demand.
Should I get a bigger pump for higher water pressure?
Not necessarily bigger HP — you need a pump rated for higher head (more stages). A pump with more impeller stages delivers higher pressure at the same flow rate without needing a larger motor. Alternatively, a constant pressure system (VFD/variable frequency drive) adjusts pump speed to maintain consistent pressure regardless of demand — the best solution for homes that want rock-solid pressure at every fixture.
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