BIZOMAT MAKEOS · Hydraulics
Pipe Flow Velocity
What is the mean velocity of this flow in a pipe of this bore?
Calculate the mean velocity of an incompressible flow in a full circular pipe from the volumetric flow and the internal bore.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Volumetric flow | L/min | Volumetric flow through the pipe. |
| Internal bore diameter | mm | Internal bore, not the nominal or outside diameter. |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Volumetric flow
- What it is
- The volume of liquid passing through the pipe each minute, for example the pump delivery or a flow-meter reading.
- Units and format
- Enter a number in L/min: litres per minute. The form accepts 0 L/min to 1000000 L/min. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 100 L/min as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Mean velocity is directly proportional to flow.
- Get it right
- Flow in m³/h converts to L/min by multiplying by 1000 and dividing by 60.
What this means: Internal bore diameter
- What it is
- The inside diameter of the pipe, the bore the liquid actually flows through. It depends on the pipe’s outside diameter and wall thickness or schedule.
- Units and format
- Enter a number in mm: millimetres. The form accepts 0.1 mm to 10000 mm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 25 mm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Velocity falls with the square of the bore: a 10 % larger bore cuts velocity by about 17 %.
- Get it right
- Nominal pipe size and outside diameter are not the bore; use the internal diameter for the actual pipe schedule or tube wall.
Method and formulas
- Flow area (mm²) = π × bore² / 4.
- Velocity (m/s) = (flow / 60,000) / (area / 10⁶).
- Example: 100 L/min in a 25 mm bore gives an area of 490.873852 mm² and a mean velocity of 3.395305 m/s.
Limitations
- Full pipe, single-phase, incompressible flow only. Mean velocity is not the peak velocity on the centreline.
- Recommended velocity limits depend on the fluid, pipe material, noise, erosion and application; none is applied here.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check a pipe or hose size against a velocity guideline
- Find the velocity for a pressure-drop calculation
- Compare bore sizes
Who it is for
- Design engineers
- Maintenance engineers
What you get
- Mean flow velocity (m/s)
- Flow area (mm²)
Interpreting the result
- For pressure drop, use this velocity in the Darcy Pipe Pressure Drop tool; the Liquid Pipe Velocity and Reynolds Number tool adds the flow regime.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 365–366. Topic reference; no source tables or recommended settings are reproduced.
- US Department of Energy, DOE-HDBK-1012/3-92, Fluid Flow — https://www.energy.gov/sites/default/files/2026-04/DOE-HDBK-1012-92_VOL3.pdf
Learn the Concepts Behind This Tool
These BIZOMAT Library readings explain the method this tool uses, with worked examples.
Method explained here · BIZOMAT original book
What a flowmeter measures
In Flow Measurement by the Numbers
What it covers: Volume, mass and standard volume flow and how to convert between them, mean velocity and Reynolds number, why temperature changes a litre, and a hot water recipe that came out 2.6% short.
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