Darcy-Weisbach equation (Pressure loss)

The Darcy-Weisbach Pressure Loss calculator compute pressure loss based on a friction coefficient, length of duct or pipe, hydraulic diameter, density and velocity of flow.

INSTRUCTIONS: Choose units and enter the following:

• (fc) Friction coefficient
• (L) Length of duct or pipe
• (hd) Hydraulic Diameter
• (ρ) Density
• (V) Velocity of flow

Pressure Loss (Δp): The pressure loss is returned in pascals.   However, this can be automatically converted to compatible units via the pull-down menu.

The Math / Science

In fluid dynamics, the Darcy–Weisbach equation is a phenomenological equation, which relates the head loss or pressure loss due to friction along a given length of pipe to the average velocity of the fluid flow. The equation is named after Henry Darcy and Julius Weisbach.

The Darcy–Weisbach equation contains a dimensionless friction factor, known as the Darcy friction factor. This is also called the Darcy–Weisbach friction factor or Moody friction factor. The Darcy friction factor is four times the Fanning friction factor, with which it should not be confused.The pressure loss (or major loss) in a pipe, tube or duct can be expressed with the Darcy-Weisbach equation below:

            Δp = λ⋅(l / d_h) ⋅ (ρ v² / 2)         

where:

• Δp is the  pressure loss
• λ is the Darcy-Weisbach friction coefficient
• l is the length of duct or pipe 
• d_h is the hydraulic diameter
• ρ is the density
• V is the mean velocity of the flow 

Related Calculators

• Head Loss
• Pressure Loss