Pipe velocity and head loss
A single straight pipe. You supply the friction factor. This does not look up a Moody chart.
Method
v = Q/A and hf = f L v² / (2 g D). Worked case: 0.02 m³/s in a 150 mm pipe is about 1.13 m/s. At f = 0.02 over 50 m, head loss is about 0.43 m.
Fittings, minor losses and a roughness lookup are not included.
Logic: how this figure is built.
How to read a pipe velocity
Velocity is discharge divided by the flowing area. Head loss on this page is the Darcy-Weisbach loss for a straight pipe: fLV²/2gD. It is a straight-pipe screen. It is not a pump curve and not a network.
Area must be the bore, not the outside diameter. A 150 mm outside pipe with a wall thickness is not a 150 mm bore. Fittings, bends and valves add loss that this page does not include.
The friction factor is an input. The page does not solve the Colebrook-White equation. If you type 0.02, the loss is the loss at 0.02. A laminar pipe and a rough pipe do not share that factor.
Use it to see whether a drawn pipe is in a sensible velocity band before a mechanical selection. A selection needs the system curve and the pump.
- Related: Reynolds number
- pipework guide
Last checked 3 October 2026. A scenario, not a design. See methodology, standards and the disclaimer.