Pipe Friction Loss Calculator
Calculate fluid pressure drop in PSI, total dynamic head loss, and water velocity in water piping using the Hazen-Williams equation.
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The Hazen-Williams Friction Loss Formula
Water flowing through piping creates friction against the inner walls. The empirical Hazen-Williams equation calculates head loss in pipes flowing full:
Hazen-Williams Equation
h_f = 0.2083 × (100 / C)^1.852 × (Q^1.852 / d^4.8655)
Where h_f is head loss (ft/100ft), C is roughness coefficient, Q is GPM, and d is inside diameter in inches.
Why Pipe Velocity Matters
Plumbing codes limit water velocity to 8.0 feet per second in cold water lines and 5.0 feet per second in hot water lines. Excess velocity causes pipe erosion, water hammer banging, and loud rushing noise behind walls.
Frequently Asked Questions
Why does PEX have slightly higher friction loss than Copper?
PEX tubing has thicker walls than copper (SDR-9 standard), resulting in a smaller internal diameter for the same nominal trade size. Additionally, standard crimp fittings insert inside the PEX tube, narrowing the bore at joints.
How do you convert feet of head to PSI?
1 PSI equals 2.31 feet of water column. To convert head loss in feet to PSI pressure drop, divide feet by 2.31 (or multiply by 0.433).
What is water hammer?
When high-velocity water is suddenly halted by a fast-closing valve (such as a washing machine solenoid), the momentum creates a hydraulic shock wave that bangs against pipe hangers. Keeping velocity under 6 ft/s prevents water hammer.