Water Distribution Pipe Sizing Calculator

Work out water distribution pipe sizing instantly with clear inputs, formula shown and shareable results.

About Water Distribution Pipe Sizing Calculator

Pipe diameter follows from continuity: area is flow divided by design velocity, and diameter from the area. Design velocity is kept at 0.6-1.5 m/s — fast enough to avoid sedimentation, slow enough to limit head loss and surge. Head loss is then checked with the Hazen-Williams equation.

Formulas

Diameter from velocity

Area = Q / v; diameter = sqrt(4 A / pi)

Hazen-Williams

S = 10.67 Q^1.852 / (C^1.852 D^4.87)

Worked example

With the default values below, Water Distribution Pipe Sizing Calculator returns Required Internal Diameter of 252.31. Change any input above and every figure here is recalculated in your browser.

Inputs used

Design Flowminimum 0 L/s: 60 L/s
Design Velocityminimum 0 m/s: 1.2 m/s
Pipe Lengthminimum 0 m: 1,500 m
Hazen-Williams C Valueminimum 1: 130

Results

Required Internal Diameter: 252.31
Flow Area: 0.050000
Hydraulic Gradient: 0.005792
Head Loss Over The Length: 8.688

Step by step

1Values used
2Diameter from velocity
3Hazen-Williams
4Required Internal Diameter= 252.31
5Flow Area= 0.050000
6Hydraulic Gradient= 0.005792
7Head Loss Over The Length= 8.688

Assumptions and limits

The result is derived only from the 4 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 6 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

Why limit velocity at both ends?

Too slow allows sediment and biofilm to accumulate and lengthens water age; too fast increases head loss with the square of velocity, raises pumping cost and worsens surge pressures on valve closure.

What C value should be used?

New ductile iron or PVC is 130-150, but unlined iron degrades to 60-100 with tuberculation. Design should use an aged value appropriate to the pipe material and expected life.