Hazen-Williams Calculator

What is the Hazen-Williams Equation?

The Hazen-Williams equation is an empirical formula widely used in civil and municipal engineering to calculate flow velocity and head loss in water supply pipes. It's simpler than Darcy-Weisbach but only applies to water at typical supply temperatures (5–25°C).

The Formula

v = 0.8492 × C × R^0.63 × S^0.54 (in m/s)

Or in terms of flow rate: Q = 0.2785 × C × D^2.63 × S^0.54 (in m³/s, D in metres)

Where:

• C = Hazen-Williams roughness coefficient (dimensionless)
• R = hydraulic radius = D/4 for full circular pipes (m)
• S = hydraulic slope = head loss / pipe length (m/m)
• D = pipe internal diameter (m)

Hazen-Williams C Values

| Pipe Material | C Value | |---------------|---------| | New smooth PVC | 150 | | Cement-lined ductile iron | 140 | | New cast iron | 130 | | 10-year-old cast iron | 110 | | Old corroded iron | 90–80 |

Practical Examples

Example: 150mm PVC pipe (C=150), 500m long, 2m head available. S = 2/500 = 0.004. Q = 0.2785 × 150 × 0.15^2.63 × 0.004^0.54 = 23.4 L/s.

Applications

Water distribution networks, fire flow analysis, irrigation main lines, and municipal infrastructure design.