Pipe Flow Calculator
Enter flow in litres per second and design velocity in metres per second. The calculation estimates bore from flow and velocity only.
A QUICK WALKTHROUGH
How to use this tool
- Enter a positive flow rate in L/s.
- Enter a positive design velocity in m/s.
- Review the estimated minimum internal bore; compare it with a manufacturer’s actual bore data.
Formula and units
The calculation converts litres per second to cubic metres per second and applies d = 2 × sqrt(Q / (π × v)). The result is an internal bore estimate in millimetres.
Important design limits
This does not calculate friction loss, pipe length, fittings, pump head, material, pressure class, wall thickness, nominal size, or standard product availability. A pipe’s nominal size is not its internal bore.
Planning aid only
Use verified system requirements and manufacturer specifications. This simple estimate is not engineering design or regulatory advice; a qualified professional should review a real water system.
GOOD TO KNOW
Common questions
Is this the nominal pipe size?
No. It estimates minimum internal bore. Check the manufacturer’s bore table and choose an appropriate available product.
Does it account for friction loss or pump capacity?
No. It uses flow and velocity only.
Are inputs uploaded?
No. The calculation runs locally in your browser.