Darcy Weisbach Equation Calculator

Head loss equals friction factor times length over diameter times velocity squared over two times gravity

Solution

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How It Works

The Darcy-Weisbach equation calculates frictional head loss in pipes by combining the friction factor, pipe geometry (length and diameter), and the velocity head (V²/2g). It works for both laminar and turbulent flow, making it the most general pipe friction formula available. The friction factor is found from the Colebrook equation or Moody chart.

Example Problem

Water flows at 2 m/s through a 200 m long, 100 mm diameter steel pipe with a friction factor of 0.02. What is the head loss?

  1. hf = f × (L/D) × (V²/2g)
  2. hf = 0.02 × (200/0.1) × (4 / 19.62)
  3. hf = 0.02 × 2000 × 0.2039 = 8.16 m

Frequently Asked Questions

What is the Darcy-Weisbach equation?

hf = f(L/D)(V²/2g) predicts pressure loss due to friction as fluid flows through a pipe. It applies to any Newtonian fluid and both laminar and turbulent regimes.

How do I find the Darcy friction factor?

For laminar flow (Re < 2,300), f = 64/Re. For turbulent flow, use the Colebrook equation or Moody chart. Our Colebrook calculator can compute this for you directly.

What is the difference between major and minor losses?

Major losses come from pipe wall friction (Darcy-Weisbach). Minor losses come from fittings, valves, and bends. In long pipelines, major losses dominate; in compact systems with many fittings, minor losses can be equally significant.

Darcy-Weisbach vs. Hazen-Williams: which should I use?

Darcy-Weisbach is more general and works for any fluid and flow regime. Hazen-Williams is simpler but only valid for water near room temperature in turbulent flow. For engineering rigor, Darcy-Weisbach is preferred.

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