Hazen-Williams Calculator
Calculate head loss, hydraulic slope and velocity for water flowing in a closed pipe with the Hazen-Williams equation — enter pipe diameter, length, flow rate and the C roughness coefficient.
Input
SI metric enters diameter in millimetres, length in metres and flow in litres/second; US customary uses inches, feet and gallons/minute.
Internal diameter of the pipe (millimetres in SI, inches in US customary).
Total length of the pipe run (metres in SI, feet in US customary).
Volumetric flow rate through the pipe (litres/second in SI, US gallons/minute in US customary).
Roughness coefficient — higher is smoother. Typical values: new PVC/plastic 150, new copper 135-140, new cast/ductile iron 130, concrete 120-130, new steel 120, old cast iron (corroded) 80-100.
Output
| Metric | Value |
|---|---|
| No data yet | |
One-line overview of velocity and head loss.
More ways to use this tool
REST API
curl -X POST https://api.iotools.cloud/v1/tool/hazen-williams-calculator \
-H "Authorization: Bearer YOUR_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"unitSystem": "si",
"pipeDiameter": "150",
"pipeLength": "500",
"flowRate": "20",
"hazenC": "130"
}'Swap in your own key from your account. The tool's fields are the body — no wrapper.
Ask an AI agent
Use the IOTools `hazen-williams-calculator` tool (Hazen-Williams Calculator) on this input:
YOUR_INPUT_HEREPaste this at any agent connected to the IOTools MCP server, then add your input.
Embed widget
<iframe
src="https://iotools.cloud/embed/hazen-williams-calculator/"
width="100%" height="520" frameborder="0" scrolling="no" loading="lazy"
title="Hazen-Williams Calculator — iotools.cloud"
sandbox="allow-scripts allow-forms allow-same-origin allow-downloads allow-popups allow-popups-to-escape-sandbox"
allow="clipboard-write"
style="width:100%;border:1px solid #e5e7eb;border-radius:12px;overflow:hidden"></iframe>
<script src="https://iotools.cloud/embed.js" async></script>Drop this into your own page — free, no key required, just a link back.
| Cost per API/MCP call | From 5 credits |
|---|---|
| Need more credits? | View pricing |
Also available with
Guides
The Hazen-Williams Calculator solves the Hazen-Williams empirical equation for head loss in a full, closed pipe carrying water — the equation civil and plumbing engineers reach for instead of the more general (and more tedious) Darcy-Weisbach approach. Enter the pipe's internal diameter, length, flow rate and roughness coefficient, and it computes velocity, head loss and hydraulic slope. It supports SI metric (millimetres, metres, litres/second) or US customary (inches, feet, gallons/minute) units.
How to use it
- Pick your unit system — SI metric or US customary.
- Enter the pipe's internal diameter, length and flow rate.
- Enter the Hazen-Williams C coefficient for the pipe material — see the typical values below.
Results update instantly. The table shows velocity, total head loss over the pipe length, and the hydraulic slope (head loss per unit length, as a percentage). A one-line summary gives velocity and head loss for quick copying.
What is the Hazen-Williams equation?
The Hazen-Williams equation relates the hydraulic slope S (head loss per unit length) of a pipe to its flow, geometry and roughness:
S = hf / L = k · Q^1.852 / (C^1.852 · D^4.8704)where Q is the flow rate, D is the internal diameter, C is the Hazen-Williams roughness coefficient (higher is smoother), L is the pipe length, and k is a unit constant: 10.67 for SI units (Q in m³/s, D in m, L in m, hf in m) or 4.727 for US customary units (Q in ft³/s, D in ft, L in ft, hf in ft). Velocity follows from continuity through the pipe's circular cross-section: V = Q / (π/4 · D²).
Unlike the Darcy-Weisbach equation, Hazen-Williams doesn't need an iterative friction-factor solution — it's valid for turbulent flow of water at ordinary temperatures, which covers the vast majority of water-distribution and plumbing design.
What C coefficient should I use?
Typical published values (new pipe, degrading with age and corrosion): PVC/plastic 150, copper 135-140, ductile or cast iron (new) 130, concrete 120-130, new steel 120, and old, corroded cast iron 80-100. A lower C means a rougher pipe and more head loss for the same flow.
Is my data private?
Completely. Every calculation runs entirely in your browser. Nothing you type is uploaded, stored or sent to a server, so you can run as many pipe checks as you like in total privacy.