Physics

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Darcy-Weisbach Calculator.

Calculate pipe head loss and pressure loss with an explicit Darcy friction factor.

On-device calculationNo signup
01

Set your values

Results update as you type.

headLoss: 4.078865 m

headLoss

0.000000m
pressureLoss: 40,000 Pa

pressureLoss

0.000000Pa

Results update automatically as you type.

This page applies only the stated idealized equation and explicit inputs; verify specialized engineering, medical, or safety decisions against applicable standards.

Use Cases

Designing a piping system

Engineers use this calculator to estimate the head loss and pressure drop in a pipe segment, which is essential for selecting pumps and determining system requirements.

Example: Calculate the pressure loss in a 100 m long, 0.2 m diameter pipe carrying water at 2 m/s with a friction factor of 0.02.

Checking existing pipeline performance

Operators can verify if a pipeline's pressure drop matches expected values, helping to identify issues like fouling or blockages.

Example: Compare measured pressure loss to calculated loss for a given flow rate and friction factor.

Frequently Asked Questions

What does the Darcy-Weisbach calculator compute?
It computes the head loss (in meters) and pressure loss (in pascals) in a pipe using the Darcy-Weisbach equation: head loss = f * (L/D) * (v²/(2g)), and pressure loss = head loss * density * gravity. You provide the Darcy friction factor, pipe length, diameter, mean velocity, fluid density, and gravity.
How is the Darcy friction factor determined?
The Darcy friction factor is a dimensionless number that depends on the flow regime (laminar or turbulent) and pipe roughness. It is typically obtained from the Moody chart or empirical correlations like the Colebrook equation. This calculator requires you to input it explicitly.
What units should I use for the inputs?
All inputs must be in SI units: pipe length and diameter in meters (m), mean velocity in meters per second (m/s), fluid density in kilograms per cubic meter (kg/m³), and gravity in meters per second squared (m/s²). The Darcy friction factor is dimensionless.

Tips & Common Mistakes

Tips

  • Ensure all units are consistent (SI units) to get accurate results in meters and pascals.
  • The Darcy friction factor is not constant; it varies with Reynolds number and pipe roughness. Use a reliable source to determine it.
  • For laminar flow (Re < 2300), the friction factor can be calculated as 64/Re, but this calculator requires you to input it manually.
  • Double-check your pipe diameter: use the internal diameter, not the nominal size, for accurate calculations.

Common Mistakes to Avoid

  • Using the wrong friction factor (e.g., Fanning friction factor instead of Darcy) – this calculator uses the Darcy friction factor.
  • Mixing units, such as entering length in feet or velocity in ft/s, which will produce incorrect results.
  • Forgetting to convert pressure loss to other units if needed – the calculator outputs in pascals (Pa).

Last updated: August 13, 2026