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Well Pump Sizing Calculator (TDH & HP)

Size submersible or jet well pumps from household demand, vertical lift, delivery pipe friction, and target system pressure — get required GPM, Total Dynamic Head, and recommended motor horsepower instantly.

Household Demand

Well Mechanics

Live Results

Recommended Pump Size

1.5 HP

Total Dynamic Head (TDH)

230 ft

Required Flow Rate

10.0 GPM

Calculated Hydraulic Workload

1.06 Calculated HP

High Dynamic Head / High Volume — High structural workload. Verify that your pressure tank's drawdown capacity matches this cycle time.

AWWA fixture baseline and bedroom minimums set required GPM. TDH sums vertical lift, pressure head (PSI × 2.31), and pipe friction. Motor HP rounds up to standard residential sizes — verify against manufacturer curves and tank drawdown before final selection.

How to Use This Well Pump Sizing Calculator

  1. Enter household demand. Set the number of bedrooms and total plumbing fixtures. The calculator applies AWWA fixture flow (1 GPM per fixture) and bedroom minimum baselines (7 GPM for 1–2 beds, 10 GPM for 3 beds, 14 GPM for 4+ beds), then uses whichever is higher as required flow.
  2. Enter well and delivery pipe details. Input vertical lift (depth to water plus any elevation to the pressure tank), total delivery pipe run length, desired system pressure in PSI, pipe diameter, and pump type (submersible or jet).
  3. Review Total Dynamic Head (TDH). TDH combines vertical lift, pressure head (PSI × 2.31), and a friction loss estimate based on pipe length and diameter. This is the total head the pump must overcome.
  4. Select the recommended motor size. Calculated HP uses the standard water horsepower formula with pump efficiency (55% submersible, 50% jet). The result rounds up to the nearest standard motor size — 0.5, 0.75, 1, 1.5, 2, or 3 HP — or flags 3.0+ HP / Commercial when calculated load exceeds 3.0 HP.

Formulas & Example

Required flow uses AWWA residential baselines. TDH sums static, pressure, and friction head. Motor horsepower follows the standard water-power equation with pump efficiency.

Fixture Flow Demand = Total Fixtures × 1.0 GPM
Bedroom Baseline: 1–2 beds = 7 GPM | 3 beds = 10 GPM | 4+ beds = 14 GPM
Required Flow Rate = max(Fixture Demand, Bedroom Baseline)

Pressure Head (ft) = Desired PSI × 2.31
Friction Loss (ft) = Pipe Length × Factor
  Factor: 3/4" = 0.20 | 1" = 0.12 | 1-1/4" = 0.05
TDH (ft) = Vertical Lift + Pressure Head + Friction Loss

Calculated HP = (GPM × TDH) ÷ (3960 × Efficiency)
  Submersible efficiency = 0.55 | Jet pump = 0.50
Motor size: round up to 0.5, 0.75, 1, 1.5, 2, or 3 HP
  > 3.0 HP → 3.0+ HP / Commercial

Worked Example

3-bedroom home, 8 fixtures, 100 ft lift, 120 ft of 1" pipe, 50 PSI target, submersible pump:

Required Flow = max(8 × 1.0, 10) = 10 GPM
Pressure Head = 50 × 2.31 = 115.5 ft
Friction Loss = 120 × 0.12 = 14.4 ft
TDH = 100 + 115.5 + 14.4 = 229.9 ft → 230 ft

Calculated HP = (10 × 229.9) ÷ (3960 × 0.55) = 1.06 HP
Recommended Motor = 1.5 HP (round up)

Switching to a jet pump (50% efficiency) on the same system raises calculated HP to about 1.16 HP — still rounding to 1.5 HP. Reducing pipe diameter to 3/4" increases friction loss and TDH, which can push the motor size up on marginal systems.

Frequently Asked Questions

What is Total Dynamic Head (TDH)?▾
Total Dynamic Head is the total equivalent height of water the pump must lift and pressurize. It equals vertical lift (static head from water level to the discharge point) plus pressure head (desired PSI converted to feet at 2.31 ft per PSI) plus friction losses in the delivery pipe. TDH is the key number for matching pump curves to your well.
How is required flow rate (GPM) determined?▾
This calculator uses two methods and takes the higher value: fixture-based demand (1 GPM per plumbing fixture per AWWA residential baseline) and bedroom minimums (7 GPM for 1–2 bedrooms, 10 GPM for 3 bedrooms, 14 GPM for 4 or more). This ensures the pump meets both fixture count and occupancy-based peak demand.
What pump efficiency should I use?▾
Submersible well pumps typically operate around 55% hydraulic efficiency in residential sizing; shallow jet pumps are closer to 50%. The calculator applies these defaults automatically. Manufacturer pump curves may show higher efficiency at the best-efficiency point — use those for final selection, but the conservative defaults here provide a safe starting motor size.
Why does pipe diameter affect friction loss?▾
Smaller pipes create more friction per foot of run. This tool uses simplified friction factors: 0.20 ft per foot for 3/4-inch pipe, 0.12 for 1-inch, and 0.05 for 1-1/4-inch. Upsizing delivery pipe reduces TDH and can drop the required motor HP on deep or long-run systems.
When do I need a commercial pump (3.0+ HP)?▾
If calculated hydraulic load exceeds 3.0 HP, the calculator flags 3.0+ HP / Commercial. Systems between 1.5 and 3.0 HP receive a high dynamic head warning — common on deep wells or high-pressure setups. Verify pressure tank drawdown, wire sizing, and pump curve data with a licensed well contractor before installing.

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