Head Loss Calculator

Calculate pressure loss along a pipe using the Darcy-Weisbach equation.

About Head Loss Calculator

Head loss rises with the square of velocity and inversely with diameter, so oversizing a pipe reduces pumping cost sharply. Converting head to pressure multiplies by density and gravity. Since loss scales with v², halving velocity by doubling pipe area cuts friction loss to about a quarter — the main lever on lifetime pumping energy.

Formula

Head Loss

h_f = f (L ÷ D) (v² ÷ 2g)

f: Darcy friction factor
L ÷ D: Pipe length in diameters

Worked example

With the default values below, Head Loss Calculator returns Head Loss of 4.0775. Change any input above and every figure here is recalculated in your browser.

Inputs used

Pipe lengthminimum 0 m: 100 m
Pipe internal diameterminimum 0 m: 0.1 m
Flow velocityminimum 0 m/s: 2 m/s
Darcy friction factoraccepts 0–0.2: 0.02
Fluid densityminimum 0.01 kg/m3: 1,000 kg/m3

Results

Head Loss: 4.0775 m
Pressure Drop: 40,000.00 Pa
Pressure Drop: 0.40000 bar
Head Loss per 100 Metres: 4.0775 m
Pumping Power per Litre per Second: 40.000 W

Step by step

1Values used
2Head Loss
3Head Loss= 4.0775 m
4Pressure Drop= 40,000.00 Pa
5Pressure Drop= 0.40000 bar
6Head Loss per 100 Metres= 4.0775 m
7Pumping Power per Litre per Second= 40.000 W

Assumptions and limits

The result is derived only from the 5 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 5 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is Head Loss calculated?

h_f = f (L ÷ D) (v² ÷ 2g) Head loss rises with the square of velocity and inversely with diameter, so oversizing a pipe reduces pumping cost sharply. Converting head to pressure multiplies by density and gravity.

Why does Head Loss matter?

Since loss scales with v², halving velocity by doubling pipe area cuts friction loss to about a quarter — the main lever on lifetime pumping energy.

What values do I need to enter?

This calculator takes 5 inputs: Pipe length, Pipe internal diameter, Flow velocity, Darcy friction factor, Fluid density. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.