PUMP
Water Pump HP Calculator for Overhead Tanks
Work out the pump HP to fill an overhead tank: flow from tank size and fill time, total head from heights and pipe friction, and the right pump size.
Assumptions used EDIT ▾
150 for PVC/CPVC, about 120 for old GI pipe.
Friction uses the Hazen-Williams formula for smooth plastic pipe, with extra length for bends and valves. Pump power = water flow × total head ÷ pump efficiency; small home pumps are often only 40–55% efficient. A surface pump can lift water only about 6–7 m on the suction side: deeper than that, use a jet or submersible pump. Check the pump's head-and-flow chart before buying.
PUMP SIZE
0.5HP
50 L/min against 17.5 m total head
- Total head3 m suction + 12 m delivery + 2.5 m friction
- 17.5 m
- Power neededAt 45% pump efficiency
- 319 W
- Water speed in pipeAbout 1–2 m/s is comfortable
- 1.50 m/s
How it’s calculated
Head = suction + delivery + pipe friction; kW = 9.81 × flow (m³/s) × head ÷ efficiency; HP = kW ÷ 0.746
Example: 1,000 L in 20 min (50 L/min), 3 m suction, 12 m delivery, 25 m of 1 inch pipe: head ≈ 17.5 m, about 0.43 HP → a 0.5 HP pump.
Questions
How deep can a normal (surface) pump pull water?+
In practice about 6–7 m on the suction side. For deeper wells or borewells use a jet pump or a submersible pump.
Why does pipe size matter so much?+
A thin pipe makes water rub harder against the walls, which adds head the pump must overcome. Going up one pipe size often lets a smaller pump do the job.
What does a foot valve do?+
It keeps the suction pipe full of water when the pump stops, so the pump does not run dry at the next start.
Is a bigger pump always better?+
No. An oversized pump wastes electricity, can cavitate and wears out faster. Choose the pump whose head-and-flow chart covers your total head.
Estimates for planning, based on the assumptions shown. They are not a guarantee of quantities or professional engineering advice; check critical work with a qualified professional.