Friction Loss Calculator

Formula

h_f = (10.67 × Q^1.852) / (C^1.852 × D^4.87) × L where Q = flow (L/s), C = Hazen-Williams coefficient, D = internal diameter (m), L = pipe length (m).

Variables

• Q — flow rate (m³/h, converted to L/s internally)
• D — pipe internal diameter (mm)
• C — Hazen-Williams roughness coefficient (140 for new PE, 130 for new steel, 100 for old galvanised)
• L — pipe length (m)

Example

85 m³/h through 200 m of new steel pipe (C=130, DN150): head loss ≈ 2.6 m. At C=100 (old galvanised), loss rises to ≈ 4.2 m.

Application

Useful for preliminary pump selection, system design and understanding pipe friction losses across water, industrial and fire-protection piping systems.

Limitations

Hazen-Williams is suitable for water at ambient temperature. It does not account for fittings, minor losses, viscosity changes or non-water fluids. Full hydraulic design requires a qualified engineer.