BuildFlo Design Guide · Water · BS 8558 / BS 6700
Cold water loading units calculator
Sum fixture loading units per BS 8558 and convert to diversified design flow. Free UK loading units calculator for pipe sizing.
What this calculator does
Loading units helps UK building services engineers with cold-water loading units from fixtures or total lu (bs 8558 / bs 6700) → design flow in l/s, m³/h and l/min. The calculation follows BS 8558 / BS 6700 methods used in everyday MEP design — enter your project inputs below for a first-pass result.
Whether you searched for "loading units", "loading units calculator", or "how to loading units", 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: LU.
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 loading units under UK standards.
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Frequently asked questions
- How do loading units convert to flow rate?
- Fixture counts are assigned loading units from BS 8558 tables, summed, then converted via the Hunter/Howick probability curve to a diversified design flow in L/s.
- When should I use BS 6700 instead of BS 8558?
- BS 8558 is the default for new UK commercial and public buildings. BS 6700 legacy tables may still apply on older specifications — confirm with the project spec.
- What is the difference between diversified and simultaneous peak flow?
- Diversified flow assumes not all fixtures run at once. Simultaneous peak (e.g. 0.1 L/s per LU) is conservative — use only when the brief requires it.
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