Pump Head and Power Calculator
Work out the total dynamic head of a pumped water system, the pump and motor power, and the NPSH available. Every step is shown with your numbers. Modelling the installation too? Browse our MEP Revit families.
Darcy–Weisbach + ColebrookCrane K values for fittingsIEC motor size in kW and hpNPSH and system curveFormula with your numbers
Flow and water
5–90 °C. Sets density, viscosity and vapour pressure.
Static head
From the lowest water level in the suction tank to the highest discharge point. Negative if the outlet is lower.
Lowest pressure in the suction vessel or main. It is subtracted from the head.
Gauge pressure at the highest point, e.g. 1.5 bar at the top fixture for a booster set. Use 0 for discharge into an open tank.
Pipework
Suction pipe
Typical value for the material. Edit for old or lined pipe.
Added to the straight-pipe friction loss. 20–50 % is a typical allowance for compact pump-room pipework.
Fittings and valves
Quantity of each item on this pipe. K = (L/D)·fT after Crane TP-410, so it changes with the pipe size.
About 2 for a clean Y-strainer (typical). Use the maker's data where you have it.
Any item not listed: meter, reducer, heat exchanger (as K).
Discharge pipe
Typical value for the material. Edit for old or lined pipe.
Added to the straight-pipe friction loss. 20–50 % is a typical allowance for compact pump-room pipework.
Fittings and valves
Quantity of each item on this pipe. K = (L/D)·fT after Crane TP-410, so it changes with the pipe size.
About 2 for a clean Y-strainer (typical). Use the maker's data where you have it.
Any item not listed: meter, reducer, heat exchanger (as K).
Pump and motor
70 % is a typical starting value. Use the pump curve at the duty point.
Typical rule: +20 % up to 7.5 kW shaft power, +15 % up to 55 kW, +10 % above.
NPSH check (optional)
Enter the pump's NPSHr at the duty flow to check the suction side. Leave it empty to skip the check.
From the pump curve.
0.5–1 m is typical. Hot water or large pumps need more.
Lowest water level minus pump centreline: positive for flooded suction, negative for suction lift.
Friction and fittings between the tank and the pump. With two pipe sections this is taken from the suction pipe.
Total dynamic head (TDH)
Enter your system to see the result.
Preliminary sizing only. Losses are for new, clean pipe and typical fitting K values; real fittings, ageing, scale and partly closed valves add more. Select the pump from the maker's curve at the duty point, check the motor against the end of the curve and confirm the design with a qualified engineer and your local code.
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Request a projectPump head in three steps
Enter flow and heights
Give the design flow, water temperature, the height from the lowest tank level to the highest outlet, and the pressure you need at the outlet.
Describe the pipework
Pick the pipe material and size for the suction and discharge pipes, enter the straight lengths and count the elbows, tees and valves, or use a percentage allowance.
Read head, power and motor
The tool adds static, friction and fitting losses into the total head, then gives hydraulic, shaft and motor power, a system curve and an optional NPSH check.
How the pump head is calculated
Total dynamic headTDH = Δz + (p_out − p_tank)/(ρg) + Σh_f + Σh_m
Pipe friction (Darcy–Weisbach)h_f = f · (L/D) · v²/(2g), with v = Q/(πD²/4) and Re = v·D/ν.
Friction factor
Colebrook–White: 1/√f = −2·log10(ε/(3.7D) + 2.51/(Re·√f)), solved by iteration. Swamee–Jain: f = 0.25/[log10(ε/(3.7D) + 5.74/Re^0.9)]². Laminar flow (Re below 2,000): f = 64/Re.
Fittingsh_m = ΣK · v²/(2g), with K = n · f_T (Crane TP-410) and f_T = 0.25/[log10(0.0457 mm/(3.7D))]².
PowerP_hyd = ρ·g·Q·H, P_shaft = P_hyd/η, motor ≥ P_shaft × (1 + margin), rounded up to the next IEC size.
NPSH availableNPSHa = (p_atm + p_tank − p_v)/(ρg) ± h_s − h_loss,suction
System curveH = Hs + k·Q², with k = (Σh_f + Σh_m)/Q² at the design flow.
Fitting loss coefficients (K)
| Fitting | K = n · f_T | K at 2 in (DN50) | K at 4 in (DN100) |
|---|---|---|---|
| Elbow 90°, standard | 30 f_T | 0.57 | 0.49 |
| Elbow 90°, long radius (r/D 1.5) | 14 f_T | 0.27 | 0.23 |
| Elbow 45°, standard | 16 f_T | 0.30 | 0.26 |
| Tee, flow through run | 20 f_T | 0.38 | 0.33 |
| Tee, flow through branch | 60 f_T | 1.14 | 0.98 |
| Gate valve, fully open | 8 f_T | 0.15 | 0.13 |
| Ball valve, full bore | 3 f_T | 0.06 | 0.05 |
| Butterfly valve, 2–8 in | 45 f_T | 0.85 | 0.73 |
| Globe valve, fully open | 340 f_T | 6.46 | 5.54 |
| Swing check valve | 100 f_T | 1.90 | 1.63 |
| Foot valve with strainer, hinged disc | 75 f_T | 1.42 | 1.22 |
| Y-strainer, clean (typical) | K ≈ 2 | 2.0 | 2.0 |
| Pipe entrance, flush / projecting | fixed | 0.5 / 0.78 | 0.5 / 0.78 |
| Pipe exit into a tank | fixed | 1.0 | 1.0 |
f_T is 0.019 for 2 in and 0.016 for 4 in Schedule 40 pipe (Crane TP-410). Default absolute roughness ε: commercial steel 0.046 mm, galvanised steel 0.15 mm, copper and PVC 0.0015 mm, PP-R and HDPE 0.007 mm, cement-lined ductile iron 0.1 mm. All roughness values can be edited in the tool.
Pump head questions
Add the height from the lowest water level to the highest outlet, the pressure needed at the outlet expressed as head, the pipe friction loss and the losses in fittings and valves. Friction and fitting losses depend on flow, so calculate them at the design flow.
Static head does not change with flow: it is the height difference plus any pressure difference between the outlet and the suction tank. Dynamic head is the friction and fitting losses, which rise with roughly the square of the flow. Total dynamic head is the sum of both.
Pressure = ρ·g·H. For water at 20 °C, 10 m of head is about 0.98 bar (98 kPa) or 14.2 psi. Hot water is lighter, so the same pressure gives slightly more head.
Hydraulic power is P = ρ·g·Q·H. For 10 L/s at 20 m of water this is about 1.96 kW. Divide by the pump efficiency for the shaft power: at 70 % that is 2.8 kW.
Add a margin to the shaft power and round up to the next standard motor size. A common rule is about 20 % for small motors up to 7.5 kW, 15 % up to 55 kW and 10 % above. Also check the power at the end of the pump curve so the motor does not overload.
NPSH available is the absolute pressure head at the pump inlet above the vapour pressure of the water. It must be higher than the pump’s NPSHr. A margin of 0.5 to 1 m is typical for cold water; hot water, suction lift and large pumps need more.
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