Sprinkler Friction Loss Calculator (Hazen-Williams)
Estimate sprinkler-pipe pressure drop with the Hazen-Williams equation from flow, C-factor, diameter, and run length.
- Enter hydraulic demand Input flow in GPM, total effective length in feet, and inside diameter in inches for the pipe segment being checked.
- Choose a C-factor Select a preset material C-factor or enter a custom value when project specs require a different roughness coefficient.
- Calculate pressure drop Press Calculate to return total friction loss (psi) and normalized loss per foot (psi/ft).
What is the Hazen-Williams equation for sprinkler friction loss?
In US customary form, pressure loss is ΔP = 4.52 × Q^1.852 × L / (C^1.852 × d^4.87), where Q is flow in GPM, L is length in feet, C is roughness coefficient, and d is inside diameter in inches. The calculator applies this form directly.
Which C-factor should I use for fire sprinkler pipe?
Use the project or standard-specified value. Typical first-pass values are around 120 for steel, 140 for ductile iron, and 150 for CPVC/plastic. Always match the value required by your design basis and AHJ expectations.
Should fittings be included in the run length?
Yes. Convert fittings and valves to equivalent length and add them to straight-pipe length before calculating friction loss; otherwise the drop will be understated.