Hazen-Williams friction loss sketches show up when you are checking a sprinkler pipe segment before you open a full hydraulic workbook. The common teaching form is p = 4.52 × Q1.85 / (C1.85 × d4.87) for psi per foot, with Q in gpm and d the actual internal diameter in inches, then multiply by length L. This page explains that sketch and gives a free browser calculator for C, Q, d, and L that reports total psi loss and psi per 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.
How friction loss is used
- Enter the Hazen-Williams C factor for the pipe (for example 120 for typical wet steel sketches—use the C your project method requires).
- Enter flow Q in gpm for the segment you are checking.
- Enter the actual internal diameter d in inches (schedule and material matter; do not substitute nominal size for ID).
- Enter the segment length L in feet (fitting equivalent lengths belong in a fuller path method, not this single-segment sketch alone).
- Compute p (psi/ft) from the formula above, then total loss = p × L. Also report p × 100 as psi/100 ft for comparison tables.
Free calculator
Educational approximation only. Formula: p = 4.52 × Q1.85 / (C1.85 × d4.87) psi/ft. Nothing you enter leaves your browser. For velocity, elevation, and pipe-size presets see the fuller Hazen-Williams calculator. For fitting equivalent lengths see equivalent length of fittings. Full multi-segment paths live in the Sprinkler Pipe Friction Loss workbook.
Worked example
A wet-pipe steel segment with C = 120, Q = 150 gpm, actual ID d = 2.067 in (2 in Sch 40), and L = 100 ft: p ≈ 0.199 psi/ft, so total friction ≈ 19.9 psi (about 19.9 psi/100 ft). 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: run velocity and elevation with the free Hazen-Williams calculator, add fittings with the equivalent length of fittings calculator, check pipe speed with the sprinkler pipe velocity calculator, and build multi-segment paths in the Sprinkler Pipe Friction Loss workbook ($29). For density/area flow sketches, see the density/area calculator.