What pipe size do I need for a given flow rate?

Enter your design flow in L/s (or derive it from loading units). The calculator selects the next standard copper trade size per BS EN 1057 and checks velocity and pressure drop against typical UK limits.

How does copper pipe sizing differ from plastic or steel?

Internal diameters and standard size ranges differ by material. Copper uses BS EN 1057 trade sizes (10–159 mm). Steel and plastic have different NB/OD tables — always confirm the material before issuing.

Can I size pipework from loading units?

Yes. Convert fixture counts to loading units per BS 8558, apply the diversified flow curve, then pipe-size at your chosen pressure-drop limit (typically 250–400 Pa/m for mains).

BuildFlo Design Guide · Water · BS EN 1057 / BS 8558

Pipe sizing calculator for UK building services

Size copper, steel, or plastic pipework from flow rate or loading units. BS EN 1057 trade sizes with BS 8558 guidance — free UK pipe sizing calculator.

What this calculator does

Pipe sizing helps UK building services engineers with size from flow or loading units - equivalent sizes across copper, steel, and plastic. The calculation follows BS EN 1057 / BS 8558 methods used in everyday MEP design — enter your project inputs below for a first-pass result.

Whether you searched for "pipe sizing", "pipe sizing calculator", or "how to pipe size", this page gives you a working tool plus the context to use it on a real job.

When to use it

Use this for early-stage sizing and sanity checks on UK building services work. It is not a substitute for issued calculations — verify against the project specification, drawings, and relevant standard before sign-off.

How to use it

1. Fill in the inputs for your scenario (defaults are starting points only). 2. Click Calculate — results include the method and assumptions where applicable. 3. Verify against the project specification and relevant standard before issuing.

Typical output unit: mm.

Tips

Defaults are indicative — replace with project-specific values from the architect, structural, or MEP spec.
For issued calculations, save results in your BuildFlo project and attach to the calculation folder.
Need the regulation citation? Open BuildFlo chat in the app and ask about pipe sizing under UK standards.

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Frequently asked questions

What pipe size do I need for a given flow rate?: Enter your design flow in L/s (or derive it from loading units). The calculator selects the next standard copper trade size per BS EN 1057 and checks velocity and pressure drop against typical UK limits.
How does copper pipe sizing differ from plastic or steel?: Internal diameters and standard size ranges differ by material. Copper uses BS EN 1057 trade sizes (10–159 mm). Steel and plastic have different NB/OD tables — always confirm the material before issuing.
Can I size pipework from loading units?: Yes. Convert fixture counts to loading units per BS 8558, apply the diversified flow curve, then pipe-size at your chosen pressure-drop limit (typically 250–400 Pa/m for mains).