Pipe friction loss calculator
Find how much pressure is lost to friction in a pipe and check that water velocity is in a sensible range.
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How it is calculated
hf = 10.67 × L × Q^1.852 / (C^1.852 × D^4.87)
Q in m³/s, D and L in m. Hazen-Williams is the standard formula for cold water in building services and irrigation. Aim for a velocity between 0.5 and 2 m/s (2–6 ft/s).
Frequently asked questions
What is the friction loss of 44 GPM in a 2 in pipe?
In PVC (C 150), about 4 m of head per 100 m (1.7 psi per 100 ft), at roughly 1.4 m/s.
What water velocity is recommended?
Between 0.5 and 2 m/s; in homes it is usually limited to about 1.5–2 m/s (5–6 ft/s) to avoid noise.