Pump · calculator
Well Pump Sizing Calculator: Required HP, GPM & TDH
Estimate required total dynamic head and hydraulic horsepower for a residential well-pump duty point.
Method record
What this calculator measures
The duty point combines flow demand with total dynamic head. Static water level is not enough; use pumping water level under expected drawdown.
TDH = pumping lift + elevation + 2.31 × PSI + friction Use it correctly
Calculation steps
- Estimate peak required GPM.
- Use pumping water level, not only static level.
- Find a pump curve crossing the calculated duty point.
Applicability
Use the model within its limits
Well yield, drawdown, casing, wire size, tank settings, pump cooling, and local requirements need qualified review.
What this result represents
- System
- Pump
- Formula
- TDH = pumping lift + elevation + 2.31 × PSI + friction
- Review
- Verify safety-sensitive work with qualified guidance.
Worked Field Example
Worked Example: Submersible Well Pump Sizing
Field Scenario: Determining TDH and motor horsepower for a 4-inch deep well supplying a 3-bathroom home requiring 12 GPM.
Given Input Parameters
Step-by-Step Mathematical Solution
- Static Lift = 140 ft + 20 ft = 160 ft.
- Service Pressure Head = 60 PSI × 2.31 = 138.6 ft.
- Total Dynamic Head (TDH) = 160 + 138.6 + 15 = 313.6 ft.
- Water Horsepower: Whp = (12 GPM × 313.6 ft) / 3960 ≈ 0.95 HP.
- Brake HP at 60% pump efficiency: BHP = 0.95 / 0.60 ≈ 1.58 HP.
Requires 12 GPM at 314 ft TDH; select a 1.5 HP or 2.0 HP deep well submersible pump.
Professional Guidance: Always verify that the well's continuous recharge rate exceeds 12 GPM to prevent running the pump dry.
Quick Answer & Key Principles
What Size Nozzle Do I Need for My Pressure Washer?
Direct Answer: Pressure washer nozzle orifice size is calculated from pump flow rate (GPM) and working pressure (PSI) using the formula: Nozzle Size = GPM ÷ √(PSI ÷ 1000).
- 2.5 GPM @ 3,000 PSI requires a Size 5.0 nozzle orifice.
- 3.0 GPM @ 3,000 PSI requires a Size 5.5 nozzle orifice.
- 4.0 GPM @ 4,000 PSI requires a Size 6.0 to 6.5 nozzle orifice.
- Warning: An undersized orifice forces excess water through the unloader valve, rapidly overheating pump packings. An oversized orifice results in weak cleaning pressure.
Engineering FAQs
Frequently Asked Questions
What is the difference between well depth, static water level, and pumping water level?
Well depth is the total drilled depth from the surface to the bottom of the casing. Static water level is where water stands naturally when the well is idle. Pumping water level (or drawdown level) is where the water column stabilizes while the pump operates continuously at full capacity; pump sizing must always be based on the pumping water level.
How many GPM does an average household need from a private well?
A standard 3 to 4-bedroom single-family home typically requires 8 to 12 GPM peak capacity. As a rule of thumb per the Water Systems Council, allocate 1 GPM per plumbing fixture or use 7 GPM for a 2-bathroom home, 10 GPM for a 3-bathroom home, and 14+ GPM for homes with irrigation systems.
What is the role of the pressure tank in a well system?
The pressure tank stores pressurized water against a compressed air bladder, providing immediate flow when a faucet opens without forcing the pump motor to start immediately. This prevents short-cycling, which degrades motor windings and capacitors.