Hazen-Williams Water Pipe Friction Calculator

The Hazen-Williams equation relates the flow of water in pressurized pipes to the friction loss caused by pipe internal wall roughness.

Unlike the Darcy-Weisbach equation, it utilizes an empirical roughness constant C independent of Reynolds number.

Flow velocity is calculated from flow rate and internal cross-sectional pipe area.

Frictional head loss varies directly with pipe length and inversely with diameter to the 4.87 power.

Smooth pipes have higher C values (140-150), whereas corroded tuberculated pipes have low C values (80-100).

Head loss in meters indicates the energy dissipation required to overcome wall friction.

Hydraulic gradient (m/km) indicates the slope of the hydraulic grade line (HGL).

Flow velocity should typically stay between 0.8 and 2.5 m/s to avoid sedimentation or excessive water hammer.

• Internal diameter: Small reductions in diameter drastically amplify head loss due to the D^4.87 power term.
• Pipe aging: Internal tuberculation and scaling reduce C factors over decades of municipal service.
• Flow velocity: High velocities above 3 m/s increase pressure transients and pumping power demands.

• Designing municipal potable water distribution networks and pumping booster mains.
• Hydraulic calculations for NFPA 13 automatic fire sprinkler systems.

• Valid strictly for water at normal ambient temperatures (5 to 30 deg C).
• Not applicable to non-Newtonian fluids, oils, slurries, or low Reynolds laminar flows.