Pipe Flow Rate Calculator

This calculator applies the Hazen-Williams flow equation, where Flow Rate scales with Pipe Diameter raised to the 2.63 power -- a much steeper relationship than the roughly square-root dependence on pressure and pipe length. That exponent is why Pipe Diameter dominates Flow Rate more than any other input: a given percentage change in diameter moves flow rate several times more than the same percentage change in Pressure or Pipe Length. Pipe Material sets the Hazen-Williams roughness coefficient C (140 for copper, 150 for PVC/CPVC and PEX, 120 for galvanized steel, which has the most internal friction of the four) and factors in linearly, so it has a comparatively modest effect next to diameter's steep exponent. Total Head Loss is a pure function of Pressure alone (2.31 feet of head per PSI) and never responds to diameter, length, or material at all.

Friction Loss per 100ft, by contrast, is driven by Pipe Length and Pressure only -- pipe diameter and material do not enter that particular output's formula at all, so treat it as a simplified estimate: it spreads Total Head Loss back over Pipe Length rather than computing a true diameter- and material-aware friction gradient, and it does not respond to flow rate either. For a diameter- and material-aware figure, use Flow Rate and Velocity above, which do account for those inputs. This is a simplified single-phase, full-pipe flow model; it does not account for fittings, valves, elevation changes, or partially-full gravity flow.