Hazen-Williams friction loss calculator

Hazen-Williams is the everyday teaching formula for friction loss in water-filled fire sprinkler pipe. The common form is p = 4.52 × Q^1.85 / (C^1.85 × d^4.87) for psi per foot, with Q in gpm and d the actual internal diameter in inches; total loss = p × L. This page focuses on choosing a C factor, entering real ID (not just nominal size), and reading psi/ft vs psi/100 ft. It is for learning and quick checks—not a substitute for the criteria adopted by your authority having jurisdiction, manufacturer pipe data, a sealed hydraulic calculation, or review by a licensed design professional. It is not a design stamp and not a PE seal.

How to use Hazen-Williams on a single segment

1. Choose the Hazen-Williams C your project method requires (for example 120 for many wet steel teaching sketches; plastic and lined systems often use higher C—follow the adopted edition and manufacturer data).
2. Enter segment flow Q in gpm.
3. Enter actual internal diameter d in inches (schedule and material matter; do not substitute nominal size for ID).
4. Enter length L in feet. Fitting equivalent lengths belong in a fuller path method (see the free equivalent length of fittings calculator), not this single-segment sketch alone.
5. Compute p (psi/ft), report p × 100 as psi/100 ft, and total = p × L.

Free calculator

Educational approximation only. Formula: p = 4.52 × Q^1.85 / (C^1.85 × d^4.87) psi/ft. Nothing you enter leaves your browser. Companion single-segment tool: friction loss calculator. Fuller presets (velocity, elevation): Hazen-Williams calculator. Darcy alternate: Darcy-Weisbach friction loss. Multi-segment paths: Sprinkler Pipe Friction Loss workbook.

Worked example

A wet-pipe steel teaching sketch with C = 120, Q = 175 gpm, actual ID d = 2.469 in (2½ in Sch 40), and L = 80 ft: compute p from the formula above, then total = p × 80. Always confirm the published internal diameter, the C factor required by your method, and check the result against the adopted edition, manufacturer data, and AHJ—not this page alone.

Next steps: compare with the free friction loss calculator or the fuller Hazen-Williams calculator, add fittings with equivalent length of fittings, check speed with the sprinkler pipe velocity calculator, and build multi-segment paths in the Sprinkler Pipe Friction Loss workbook ($29).