New HDPE/PVC ≈ 150, steel ≈ 120, hose ≈ 130. Lower for old or rough pipe.
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How it's calculated
- Velocity: V (ft/s) = 0.4085 × Q (USGPM) / d² (in). Velocity head = V²/2g.
- Hazen-Williams: hf (ft) = 0.002083 × L × (100/C)1.852 × Q1.852 / d4.8655. Friction per 100 ft equals friction per 100 m in head terms (both are m/100 m = ft/100 ft).
- HDPE uses the average inside diameter, OD − 2.12 × OD/DR. Steel and PVC use schedule inside diameters; hose uses nominal ID.
- Valid for water at ordinary temperatures in turbulent flow. Single pipe run only: no fittings, static head or pressure. See the disclaimer.
Related: HDPE pipe dimensions · unit converter · how to calculate TDH
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