Friction Loss Calculator

This calculator works out the friction loss in a straight run of full pipe from the flow rate, the inside diameter, the length and the pipe material. For water it solves Darcy-Weisbach with a Colebrook-White friction factor and runs Hazen-Williams alongside it, reporting the head loss in feet and metres, the pressure drop in psi and kPa, the velocity, the Reynolds number and how far the two methods land apart. A second action takes your own density and viscosity for any other fluid. Fittings, valves and bends are not included, and on a short run they often add more loss than the pipe does.

Calculator Type
Flow Measured In
Diameter Measured In
Length Measured In
Temperature Measured In
The two figures are the published constants for the material, not measurements: e is the absolute roughness off a Moody or Colebrook table, tabulated in millimetres everywhere including in the United States, and C is the dimensionless Hazen-Williams coefficient. They stay as they are whichever units you picked for the flow, the diameter and the length.
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Flow Measured In
Diameter Measured In
Length Measured In
Millimetres, because that is how a Moody or Colebrook table prints absolute roughness, so the length and diameter controls above deliberately do not reach this box. Drawn plastic and copper 0.0015, new steel 0.045, galvanised 0.15, aged cast iron 0.26, concrete 0.3 to 3. An older American handbook gives the same figures in feet, 5e-6 ft for drawn tube, which is 0.0015 mm.
Kilograms per cubic metre, which is the only unit a published fluid density is written in, so there is nothing to choose here. Water near 998, light oil 850, air at sea level 1.2.
Centistokes, which is the unit every fluid data sheet and every ISO viscosity grade uses, and it is already metric: 1 cSt is 1 mm2/s exactly. Water at 20 C is 1.004 cSt, SAE 30 oil near 100 cSt, air near 15 cSt.
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