Pump Head Calculator

Add up lift, pipe friction and outlet pressure to get the total dynamic head, then the horsepower the pump needs.

From the water surface you pump from up to the outlet.
0 if it just spills into a tank.
Small pumps run about 40% to 70%.
Pipe Friction
Pipe
Suction and discharge, plus fitting allowances.
PVC 150, copper 140, steel 120.
Fractions and decimals both work.
–
Feet TDH
Lift
Friction
Pressure head
TDH in PSI
Water horsepower
Pump horsepower
Pipe velocity
Motor Size

Pump Duties

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PumpGPMTDH (Ft.)HPRemove

How to Calculate Pump Head

Total dynamic head (TDH) is everything the pump has to push against, expressed in feet of water: the height it lifts the water, the friction in the pipe, and any pressure you need at the end.

TDH (ft) = vertical lift + friction loss + outlet pressure (psi) × 2.31
Water horsepower = gpm × TDH ÷ 3,960   Pump horsepower = water hp ÷ efficiency

Friction loss here uses the Hazen–Williams equation (see the friction loss calculator). The 3,960 comes from 33,000 ft·lb per minute in a horsepower divided by 8.33 lb per gallon of water.

Worked Example

Reading a Pump Curve

Pump makers publish a curve of flow against head. Find your flow along the bottom and your TDH up the side: the pump you choose should put that point on or just above its curve, near the middle of the curve where efficiency is best. Well pumps and booster pumps are usually rated this way.

Tips

For suction lift (pump above the water), keep the lift well under about 20 feet at sea level and check the pump's NPSH requirement. Add equivalent lengths for elbows, check valves and foot valves to the pipe length. Round the motor up to the next standard size.