Perda de Carga (Darcy-Weisbach)
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
Darcy-Weisbach
About this calculator
The Darcy-Weisbach head loss calculator determines the energy loss in pipes due to friction. It uses the formula h_f = f·(L/d)·(v²/2g), where h_f is head loss (m), f is the Darcy friction factor (dimensionless), L is pipe length (m), d is inner diameter (m), v is average fluid velocity (m/s), and g is gravity (9.81 m/s²). The factor f depends on flow regime (laminar or turbulent) and pipe roughness.
To use the tool, you input the volumetric flow rate (in m³/s or L/s) and pipe properties. The calculator converts flow to velocity, computes the Reynolds number to determine regime, and estimates f using appropriate equations (e.g., Colebrook-White for turbulent). The result is the total head loss, essential for pump and hydraulic system sizing.
This calculator is useful for engineers and technicians in water supply, sewage, irrigation, building, and industrial projects. For example, when designing a 100 m pipe with 50 mm diameter carrying water at 2 L/s, you can check if the head loss is acceptable for the available pump.
Important caveats: the formula assumes steady, incompressible flow, Newtonian fluid, and full pipe. For highly viscous liquids or gases, corrections may be needed. Also, the friction factor depends on relative roughness; typical values for commercial pipes (steel, PVC, copper) can be used, but manufacturer data improves accuracy.
Frequently asked questions
What is the Darcy friction factor and how is it calculated?
The Darcy friction factor f is a dimensionless number representing flow resistance due to pipe wall friction. For laminar flow (Reynolds < 2000), f = 64/Re. For turbulent, the Colebrook-White equation is used, depending on Reynolds number and relative roughness.
Can I use this calculator for gases?
Yes, as long as the gas is treated as incompressible (small density variation) and head loss is small relative to absolute pressure. For large pressure drops, specific compressible flow formulas are recommended.
What is the difference between major and minor head loss?
Major head loss (calculated here) occurs along straight pipe due to friction. Minor head loss occurs at fittings, valves, and bends. For complete systems, add both.
How do I get the pipe roughness value?
Typical values: commercial steel 0.045 mm, PVC 0.0015 mm, copper 0.0015 mm, concrete 0.3-3 mm. Consult engineering tables or manufacturer data for better accuracy.
Does the calculator account for water viscosity?
Yes, water kinematic viscosity at 20°C is assumed as 1e-6 m²/s. For other temperatures, results may vary. If needed, input a custom value (future feature).