Hazen-Williams Calculator

Calculate pipe flow velocity and head loss using the empirical Hazen-Williams formula for water distribution systems.

Pipe Networks · Empirical

C Coefficient Presets

C decreases with pipe age and scale buildup. Always verify against site measurements for older systems.

Inputs

H-W C coefficient C (—)

Internal diameter D (mm)

Rₕ = D/4 = 0.02500 m

Hydraulic slope S (m/m)

S = hf / L (head loss per unit length)

Theory

Hazen-Williams Formula (SI)

V = 0.8492 × C × Rₕ^0.63 × S^0.54

Rₕ in m, V in m/s, S dimensionless (m/m)

US Customary Form (different constant)

V = 1.318 × C × Rₕ^0.63 × S^0.54

Rₕ in ft, V in ft/s — do NOT mix with SI inputs

Hydraulic Radius — Circular Pipe

Rₕ = A / P = (πD²/4) / (πD) = D/4 (full-flow circular pipe)

Variables

C — Hazen-Williams roughness coefficient (dimensionless)
Rₕ — hydraulic radius = A/P [m]
S — hydraulic slope = hf / L [m/m]
V — mean flow velocity [m/s]

Typical C Values

Pipe material / condition	C (typical)
PVC / polyethylene (new)	140–150
Fiberglass (new)	140–150
Steel (new, smooth)	130–140
Cast iron (new, unlined)	120–130
Concrete (smooth)	110–140
Galvanized steel	100–120
Cast iron (old, some scale)	80–100
Heavily corroded / tuberculated	60–80

The Hazen-Williams formula is empirical and valid only for water near ambient temperature. For other fluids or precise engineering calculations use the Darcy-Weisbach equation with the Colebrook-White or Swamee-Jain friction factor.