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Domestic Water Pipe Friction Loss Calculator (Hazen-Williams)

Calculate the friction head loss in a domestic water supply pipe run using the Hazen-Williams formula.

Computed in your browser — nothing you enter is uploaded. Figures are presented for United States against IRC 2024, and every formula is cited under regulatory standards below.

Last verified 2026-08-27 · v1.1.0

Market
Imperial · sales tax
164 ft
Schematic, drawn to the proportions you entered — not to scale on screen.

Friction head loss

19.41 ft

High confidence

For the dimensions entered, expect a friction head loss of 5.92 m. Set for United States against IRC 2024. The market selector changes both the units and the code cited.

Estimated cost — your price

This site holds no price list for this material — local prices vary too much to publish honestly. Enter your supplier's price and the result is costed with it.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — confirmed fixes become pinned regression tests.

[Schema Verified] Computed in alignment with American Concrete Institute (ACI 318-19) formulas and International Residential Code (IRC 2024) spatial boundaries.

Regulatory standards & verification citations

  • Hazen-Williams equation (SI units): hf = 10.67 × L × Q^1.852 ÷ (C^1.852 × D^4.8704), where L is pipe length (m), Q is flow rate (m³/s), C is the Hazen-Williams roughness coefficient, and D is the pipe's internal diameter (m)

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Frequently asked questions

What does the Hazen-Williams C coefficient represent?
It's an empirical roughness coefficient for the pipe material and condition — smoother pipes like new copper or plastic use a higher C (around 150), while older or rougher steel pipe uses a lower C (around 140), which increases the calculated friction loss.
Why does pipe diameter have such a large effect on the result?
The Hazen-Williams equation raises diameter to the power of 4.8704 in the denominator, so even a modest reduction in internal diameter causes a much larger increase in friction head loss for the same flow rate.
Does this calculator include losses from fittings and valves?
No — this calculates straight-pipe friction loss only, based on the Hazen-Williams equation. Fitting and valve losses should be added separately, typically by converting them to an equivalent length of straight pipe.