Pump Head Calculator
Static lift plus losses, giving total head and shaft power.
Quick answer
With the default inputs: Static head 20 · Design flow 10 m³/h · Pipe length 50 etc.Total head required 33.75 m
Edit the inputs below to recalculate.Inputs
Result
Total head required
33.75m
| Static head | 20.00m |
| Pipe velocity | 1.41m/s |
| Reynolds number | 70,314 |
| Friction factor λ | 0.0283 |
| Friction loss | 2.88m |
| Minor loss | 0.86m |
| Outlet pressure head | 10.00m |
| Losses share | 11.1% |
| Shaft power | 1.41kW |
| Suggested motor | 1.63kW |
| Outlet pressure | 0.331MPa |
Head is not how high the pump can push but total head: static lift plus all losses plus residual pressure at the outlet. Sizing on storey height alone and ignoring pipe loss and discharge pressure is why top floors run short of pressure. Shaft power is ρgQH/η and the motor needs another 10-15%. The duty point must sit in the efficient band; outside it energy use climbs sharply.
Reverse: known result, work out one input
Enter a target result; the other inputs stay fixed and this one is worked out.
Formula
| Velocity | Q ÷ A with Q in m³/s |
| Reynolds number | Re = vd ÷ ν, ν = 1.006×10⁻⁶ m²/s at 20°C |
| Friction factor | λ from Swamee-Jain, ε = 0.15 mm for steel |
| Friction loss | λ × (L ÷ d) × (v² ÷ 2g) |
| Minor loss | friction × share |
| Total head | static + friction + minor + outlet pressure |
| Shaft power | ρgQH ÷ η |
| Pressure | 1 MPa ≈ 102 m of water |
20 m static, 10 m³/h through 50 m of 50 mm bore with 10 m outlet pressure at 65% efficiency: 1.41 m/s, Re about 70,300, λ = 0.0283, 2.88 m friction, 0.86 m minor, 33.75 m total head and 1.41 kW shaft power — a 1.63 kW motor.
How to work it out
- Establish the static head hs: the elevation difference from the suction water level (lowest level in the tank) to the highest outlet. It is a difference in level, not a pipe length. Confusing the two is where most schemes go wrong first.
- Convert the flow to m³/s (1 m³/h is 1/3600 m³/s) and compute velocity v = Q ÷ A.
- Work out Reynolds number Re = v × d ÷ ν (ν = 1.006×10⁻⁶ m²/s at 20°C) and get the friction factor from Swamee-Jain. Use ε = 0.15 mm for steel and about 0.2 mm for galvanised.
- Friction loss hf = λ × (L÷d) × (v²÷2g), plus minor losses at 20-40% of friction — the upper end where valves and elbows are numerous.
- Total head H = hs + hf + minor + required outlet pressure. 1 MPa is about 102 m of water, so 0.1 MPa is 10.2 m.
- Shaft power P = ρgQH ÷ η with ρg = 9800 N/m³ and η at 60-75% (low for small pumps, high for large), then apply 1.1-1.2 for motor selection.
Where it goes wrong
- Sizing head from building height alone. Six storeys at 18 m does not mean a 20 m pump: add 8-10 m of pipe loss and 10 m of outlet pressure, or the pump cannot deliver and terminal taps dribble.
- Treating pipe length as head. Horizontal pipe produces friction only, no static head; adding horizontal distance straight into the head figure overstates it badly and buys an oversized pump that runs inefficiently forever.
- Computing power at 100% efficiency. The motor then comes out at half the required rating, the pump runs continuously overloaded and the winding burns.
- Ignoring suction lift. A self-priming pump loses suction beyond 7-8 m (the theoretical 10.33 m must be reduced for NPSH and pipe losses), so the installation has to become flooded suction or the pump moved down.
Material and cost
Domestic boosters are 300-800 CNY, small inline pumps 800-2500, multistage centrifugal sets for tall buildings 3000-20,000. Going one size up raises power draw proportionally; an extra 10 m of head costs a few hundred CNY a year in electricity, overtaking the pump price difference within three years.
On site
- Select on the operating point where the system resistance curve crosses the pump curve, not on the catalogue duty point. Running far out on the right of the curve causes cavitation.
- Variable-speed pumps cost 30-50% more but save over 30% of energy at part load. For residential boosters, variable speed is essentially the default choice.
- Allow at least 5D of straight pipe at the suction. Mounting a pump right against an elbow or valve causes air entrainment — noisy, low flow, and an impeller that erodes through quickly.
- Fit a check valve and flexible connector at the discharge. Without the check valve, reverse flow on shutdown produces water hammer that cracks fittings and flanges.
Basis
- GB 50015-2019 Standard for design of building water supply and drainage, booster equipment and pump rooms
- GB 19762-2007 Minimum allowable values of energy efficiency for centrifugal pumps
FAQ
Why does pump head always come up short?
Three reasons: sizing on storey height without pipe loss, where 50 m at 1.4 m/s costs 2.5 m and fittings push it to 3.5; ignoring residual pressure, since a shower needs 0.1-0.15 MPa or 10-15 m; and reading the shut-off head off the nameplate, which at the actual duty point is 20-30% lower.
Variable speed or fixed speed?
Variable speed where demand swings. It matches speed to load and power falls with the cube of speed, saving 30-50%, while a fixed-speed unit can only start and stop, wearing the motor and swinging the pressure. It costs 50-100% more up front and brings harmonics. Domestic water and chilled water favour variable speed; fire pumps must be fixed — codes do not allow it.
What causes cavitation?
When pressure at the suction falls below the vapour pressure of water, bubbles form and collapse in the high-pressure zone, sending shock waves at thousands of atmospheres into the impeller. It shows as noise, vibration, falling flow and a pitted, honeycombed impeller. Prevent it with a lower suction lift, a larger suction pipe, fewer inlet bends and adequate NPSH margin.
Cite this page
Use this format in reports, method statements or coursework. The link is permanent.
Building Calculator. Pump Head Calculator. 2026-10-25. https://jianzhujisuan.com/en/pump-head
Results are estimating aids only and are not a design basis. Construction and final accounts must follow the drawings, the applicable standards and an approved method statement. Anything affecting structural safety, shoring or falsework must be checked by a suitably qualified engineer.