# Pump Head Calculator

Static lift plus losses, giving total head and shaft power.

- Page: https://jianzhujisuan.com/en/pump-head
- Category: M&E (https://jianzhujisuan.com/en/c/me)
- Chinese version: https://jianzhujisuan.com/zh/pump-head.md
- Data checked: 2026-10-25

## Quick result

With the default inputs (Static head 20 m, Design flow 10 m³/h, Pipe length 50 m, Pipe bore 50 mm, Minor loss share 30%, Required outlet pressure 10 m, Pump efficiency 65%): **Total head required 33.75 m**

## Inputs

| Parameter | Type | Default | Unit | Note |
|---|---|---|---|---|
| Static head | number | 20 | m | Vertical rise from suction level to outlet |
| Design flow | number | 10 | m³/h |  |
| Pipe length | number | 50 | m |  |
| Pipe bore | number | 50 | mm |  |
| Minor loss share | number | 30 | % |  |
| Required outlet pressure | number | 10 | m | 0.1 MPa equals about 10 m of head |
| Pump efficiency | number | 65 | % |  |

## 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

## Worked example

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.

## Questions

### 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.

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