Well Pump HP Sizing: How Much Horsepower Do You Need?
📋 In This Guide
Factors That Determine HP
1. Well Depth
- Deeper wells need more HP
- Pump must lift water higher
- Every 2.31 feet of lift = 1 PSI
2. Water Level (Pumping Level)
- Where water sits when pumping
- Not the same as well depth
- This is the actual lift required
3. Required Flow Rate (GPM)
- More GPM = more HP needed
- Typical home: 8-12 GPM
- With irrigation: 15-25 GPM
4. Desired Pressure
- Higher pressure = more HP
- Standard: 40-60 PSI
- 50-70 PSI needs more pump
5. Pipe Friction
- Long runs add resistance
- Small diameter = more friction
- Fittings add friction
Total Dynamic Head (TDH)
TDH = Pumping Level + Pressure Required + Friction Loss
- Convert pressure to feet: PSI × 2.31
- Add all factors together
- This tells you pump requirements
How to Calculate
Example Calculation
| Pumping water level: | 150 feet |
| Pressure (60 PSI): | 139 feet (60 × 2.31) |
| Friction (estimated): | 20 feet |
| Total Dynamic Head: | 309 feet |
Find Pump on Performance Curve
- Look at manufacturer curves
- Find GPM at your TDH
- Select pump that delivers needed GPM at that TDH
Rule of Thumb
For a rough estimate (not engineering precision):
- Shallow well (under 80 ft): 1/2 HP
- Medium well (80-150 ft): 3/4 HP
- Deep well (150-300 ft): 1-1.5 HP
- Very deep (300-500 ft): 1.5-2 HP
- Extremely deep (500+ ft): 2-3+ HP
These assume moderate flow and standard pressure.
Quick Sizing Guide
Residential Pumps
| HP | Typical TDH | Application |
|---|---|---|
| 1/2 HP | 100-150 ft | Shallow wells, low demand |
| 3/4 HP | 150-250 ft | Most residential |
| 1 HP | 200-350 ft | Medium-deep, moderate flow |
| 1.5 HP | 300-450 ft | Deep wells, higher flow |
| 2 HP | 400-550 ft | Very deep, irrigation |
| 3 HP | 500-700 ft | Large homes, agriculture |
GPM Considerations
- Same HP delivers less GPM at higher TDH
- Need more GPM? May need more HP
- Check pump curves, not just HP rating
2-Wire vs 3-Wire
- Under 1.5 HP: Usually 2-wire
- 1.5 HP and up: Often 3-wire (control box)
- 3-wire easier to troubleshoot
Sizing Problems
Undersized Pump
- Insufficient pressure or flow
- Pump runs constantly
- Can't keep up with demand
- Motor overheating
Oversized Pump
- Short cycling (on/off rapidly)
- Premature wear
- Higher electric bills
- May outpace well recovery
- Risk of running dry
Signs of Wrong Size
- Pump cycles frequently (less than 1 min)
- Can't run multiple fixtures
- Pressure drops significantly during use
- Water runs out (pumping faster than well recovers)
When to Upsize
- Adding irrigation
- Building addition
- Multiple bathrooms
- Pool filling needs
We service all major pump brands including Franklin Electric, Grundfos, Goulds (Xylem), and Sta-Rite (Pentair). Our trucks carry common parts and components for same-day repairs.
Frequently Asked Questions
What size well pump do I need?
Depends on well depth, water level, required GPM, and pressure. Calculate TDH and match to pump curve. Most residential: 3/4 HP to 1.5 HP.
Is a bigger well pump better?
No—oversized pumps cycle too much, wear faster, and can outpace well recovery. Proper sizing is key.
How do I know if my pump is too small?
Signs: low pressure, pump runs constantly, can't run multiple fixtures. Proper sizing calculation confirms.
Can I replace my pump with a bigger one?
Maybe—but consider well yield. Bigger pump won't help if well can't produce more water. May need larger pressure tank instead.
What HP for a 400-foot well?
Typically 1.5-2 HP, depending on water level and required GPM. Calculate TDH for accuracy.
Need Pump Sizing Help?
We calculate proper pump size based on your well specs and water needs.
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