Calculate friction loss in a pipe or hose using the Hazen-Williams equation. Enter your flow rate (GPM), pipe/hose length (ft), pipe inner diameter (in), and Hazen-Williams C coefficient to get the friction head loss (ft) and pressure drop (PSI) instantly. A breakdown chart shows how pipe dimensions and flow rate contribute to the result.
Friction Loss
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Head Loss
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Flow Velocity
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Friction Loss per 100 ft
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Friction loss is the reduction in fluid pressure (or energy head) caused by the resistance between the flowing fluid and the inner walls of a pipe or hose. It increases with flow velocity, pipe length, and pipe roughness, and decreases with larger pipe diameters.
This calculator uses the Hazen-Williams equation: H_L = 10.67 × L × Q^1.852 / (C^1.852 × D^4.87), where H_L is head loss in feet, L is pipe length in feet, Q is flow rate in cubic feet per second, C is the Hazen-Williams roughness coefficient, and D is the inner diameter in feet. It is widely used for water distribution systems.
The C coefficient represents the smoothness of a pipe's interior surface. Higher values mean smoother pipes and less friction loss. Typical values: PVC = 150, copper = 140, new steel = 120, galvanized iron = 110, cast iron = 100. Older or rougher pipes have lower C values.
Friction in a pipe causes a drop in pressure (or head) along the pipe length. This means the pressure at the outlet is lower than at the inlet. In practical systems like fire hoses or water supply networks, this loss must be accounted for to ensure adequate pressure at the delivery point.
The four main factors are: (1) flow rate — higher flow increases friction loss significantly; (2) pipe length — loss is directly proportional to length; (3) pipe diameter — smaller diameters cause much greater friction loss; and (4) pipe material/roughness — rougher surfaces have lower C values and higher friction loss.
You can reduce friction loss by increasing the pipe diameter, using smoother pipe materials (higher C coefficient), reducing the total pipe length where possible, and minimizing the number of fittings and bends. For fire hose applications, using larger diameter hose dramatically cuts friction loss.
No — the Hazen-Williams formula was specifically developed for water flowing at typical temperatures (around 60°F / 15°C). For other fluids, highly viscous liquids, or very high or low temperatures, the Darcy-Weisbach equation combined with the Moody chart is more appropriate.
Pressure in PSI is calculated from head loss in feet using the relationship: PSI = head loss (ft) × 0.4335. This conversion assumes water at standard conditions (density ≈ 62.4 lb/ft³).