Water Velocity In Pipe Calculator

Work out water velocity in pipe instantly with clear inputs, formula shown and shareable results.

About Water Velocity In Pipe Calculator

Velocity is volumetric flow divided by cross-sectional area. The Reynolds number, velocity times diameter divided by kinematic viscosity, confirms the flow regime: water in building services is almost always fully turbulent, above 4000, which is why turbulent friction correlations apply.

Formulas

Velocity

V = Q / A, A = pi D² / 4

Reynolds number

Re = V D / kinematic viscosity, about 1.0 x 10^-6 m²/s for water at 20 °C

Worked example

With the default values below, Water Velocity In Pipe Calculator returns Flow velocity of 0.6366. Change any input above and every figure here is recalculated in your browser.

Inputs used

Flow rateminimum 0.01 L/s: 5 L/s
Internal diameterminimum 5 mm: 100 mm

Results

Flow velocity: 0.6366 m/s
Cross-sectional area: 7,854.0 mm²
Flow rate in cubic metres per hour: 18.000 m³/h
Reynolds number: 63,662

Step by step

1Values used
2Velocity
3Reynolds number
4Flow velocity= 0.6366 m/s
5Cross-sectional area= 7,854.0 mm²
6Flow rate in cubic metres per hour= 18.000 m³/h
7Reynolds number= 63,662

Assumptions and limits

The result is derived only from the 2 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 4 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 the Water Velocity In Pipe figure worked out?

V = Q / A, A = pi D² / 4. Velocity is volumetric flow divided by cross-sectional area.

What velocity is too high?

Above roughly 2 m/s copper and steel pipes become audible, and above 3 m/s erosion-corrosion becomes a real risk, particularly at bends and in soft water.

What values do I need to enter?

This calculator takes 2 inputs: Flow rate, Internal diameter. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.