Well Pump Sizing Calculator (GPM, TDH & Horsepower)
Calculate exact submersible well pump horsepower, Total Dynamic Head (TDH), pipe friction loss, pressure tank volume, and submersible cable wire gauge under Hydraulic Institute and National Electrical Code standards.
Min 10 Gal Drawdown (provides safe 60s motor cycle)
Cross-sectional engineering diagram: Well casing, dynamic water level, submersible pump, pitless adapter, and residential pressure tank assembly.
Dedicated Well Pump Engineering Calculators & Reference Guides
Select a specialized sizing guide for in-depth formulas, friction matrices, and electrical charts:
How to Calculate Total Dynamic Head (TDH) for a Deep Well
Total Dynamic Head represents the total equivalent height and mechanical resistance a submersible well pump must overcome to deliver water at your desired household pressure. Sizing a pump on depth alone without calculating TDH leads to weak water pressure or burned-out motors.
Total Dynamic Head (Feet) = Pumping Water Level + Elevation Rise + Pipe Friction Loss + Pressure Head
- 1. Pumping Water Level: The vertical depth in feet from the wellhead down to the water surface while the pump is actively operating (static water level plus drawdown depth).
- 2. Elevation Rise: The vertical distance in feet from the top of the well casing up to the pressure tank or highest plumbing fixture in your home.
- 3. Pipe Friction Loss: Resistance created by water moving against the pipe walls. Modeled accurately via the Hazen-Williams equation based on flow rate (GPM), pipe material, and internal diameter.
- 4. Pressure Head: Converting your pressure tank cut-out threshold into equivalent feet of water column. Because 1 PSI = 2.31 feet of head, a standard 40/60 PSI switch requires 60 × 2.31 = 138.6 feet of head.
Submersible Well Pump Horsepower & Wire Sizing Reference
| Motor HP | Voltage | Typical Flow | Max TDH Head Range | Max Cable Run (12 AWG) | Breaker |
|---|---|---|---|---|---|
| 0.5 HP (1/2 HP) | 230V 1-Ph | 5 – 10 GPM | 150 – 250 ft | 650 ft | 15A |
| 0.75 HP (3/4 HP) | 230V 1-Ph | 8 – 12 GPM | 220 – 340 ft | 480 ft | 15A |
| 1.0 HP (1 HP) | 230V 1-Ph | 10 – 15 GPM | 280 – 420 ft | 400 ft | 20A |
| 1.5 HP (1-1/2 HP) | 230V 1-Ph | 10 – 20 GPM | 350 – 540 ft | 310 ft | 25A |
| 2.0 HP (2 HP) | 230V 1-Ph | 15 – 25 GPM | 420 – 680 ft | 250 ft | 30A |
| 3.0 HP (3 HP) | 230V 1-Ph | 20 – 35 GPM | 550 – 850 ft | 120 ft (Use 10 AWG) | 40A |
Frequently Asked Questions About Well Pump Sizing
How do I calculate Total Dynamic Head (TDH) for a well pump?
Total Dynamic Head (TDH) is the total equivalent feet of vertical lift and resistance the pump must overcome. The formula is: TDH = Pumping Water Level (Depth to water during pumping) + Elevation Lift (Rise from wellhead to pressure tank) + Pipe Friction Loss (Resistance in drop pipe and horizontal run) + Pressure Head (Operating pressure cutoff PSI × 2.31 ft/PSI).
What size well pump horsepower (HP) do I need for my house?
Most 3 to 4 bedroom residential homes with 2 to 3 bathrooms require an 8 to 12 GPM pump powered by a 0.75 HP (3/4 HP) or 1.0 HP submersible motor. For deep wells exceeding 250–350 feet or high-demand homesteads with lawn irrigation, a 1.5 HP to 3.0 HP motor is required to overcome high Total Dynamic Head.
What is the difference between a 2-wire and 3-wire well pump?
A 2-wire submersible pump has its starting capacitor, relay, and thermal protection built directly inside the submerged motor casing. A 3-wire pump uses three insulated power conductors running to an external control box mounted on the surface inside your home or utility room. 3-wire systems are easier to maintain because worn-out starting capacitors can be replaced without pulling hundreds of feet of pipe from the well.
How do I size a pressure tank for my well pump?
A pressure tank is sized based on the pump's GPM flow rate and motor run cycle time. Submersible motors require a minimum run cycle of 60 seconds (for motors up to 1.5 HP) or 120 seconds (for motors 2 HP and larger) to prevent rapid short-cycling and premature motor burnout. Minimum Drawdown = Flow (GPM) × Run Time (Minutes). At 40/60 PSI, a 10 GPM pump requires a pressure tank with at least 10 gallons of drawdown, which translates to a ~32 to 36 gallon gross tank volume.
What size wire gauge (AWG) is required for a submersible well pump?
Submersible pump wire size depends on motor horsepower, supply voltage (115V vs 230V), and total circuit length (depth in the well plus distance to the electrical panel). For a typical 1 HP 230V motor, 14 AWG copper wire is permitted up to 250 feet, 12 AWG up to 400 feet, and 10 AWG up to 630 feet to keep continuous voltage drop under the recommended 5% limit.