Engineer Tools & Resources
Quick, reliable calcs for clean-water pipework. Hazen–Williams & Darcy–Weisbach, velocity & sizing helpers, head/pressure converter, and reference tools — all in one place.
Pipe Headloss Calculator
For clean, cold water (~4–24°C), Hazen–Williams is common. For other fluids or higher accuracy, use Darcy–Weisbach.
HW (SI): h = 10.67 · L · Q^1.852 / (C^1.852 · D^4.8704)
Velocity ↔ Flow helper
Quickly check velocity for a given pipe & flow.
Head ↔ Pressure
FAQs & Notes
When is Hazen–Williams appropriate?
Use for clean, cold water (typically 4–24°C) in full pipes, under turbulent flow conditions. It’s quick, simple, and widely used in water industry calculations, but it is not accurate for hot water, viscous liquids, or other fluids.
When should I use Darcy–Weisbach instead?
Darcy–Weisbach works for any fluid, temperature, and condition when you know (or can estimate) the friction factor. It is the preferred method in standards and is especially important for hot or chilled water, seawater/chemicals, large diameter pipelines, or high velocities.
How accurate are these calculations?
Accuracy depends on diameter, flow, C/roughness, and fittings. Hazen–Williams is typically within ±5–10% for its intended use; Darcy–Weisbach can be closer if properties are known.
How do I convert head to pressure?
Use the converter above. 1 m of water ≈ 9.81 kPa ≈ 0.098 bar ≈ 1.42 psi.
What velocity should I aim for?
Common targets: 1.5–3 m/s (building services), 1–2.5 m/s (irrigation), 2–3.5 m/s (cooling). Avoid excessive noise/erosion.
© Henry Pumps — Built for engineers. This page is a helper; always verify design assumptions for your application.