BS 8500 and BS EN 206 — how concrete is actually specified

What these standards are

Concrete is specified, not guessed, and the two documents that do the work are:

• BS EN 206 — the European standard for concrete. The approved documents cite it as "BS EN 206-1. Method of specifying and guidance for the specifier" and, in its companion part, "BS EN 206-1. Specification for constituent materials and concrete".
• BS 8500 — the British Standard that sits alongside it, in two parts: BS 8500-1, "Method of specifying and guidance for the specifier", and BS 8500-2, "Specification for constituent materials and concrete".

In other words BS EN 206-1 supplies the framework and BS 8500-1 and -2 are the UK's complementary documents that make specification practical in a British context — which is exactly the wording the British Standard's own title uses: "Concrete. Complementary British Standard to BS EN 206-1".

Where the regulations send you

This is not a nice-to-have. Approved Document A lists BS 8500-1 and BS 8500-2 in its Section 1 references, and Approved Document C uses them directly:

• AD C paragraph 4.14(a)(i) requires a suspended timber floor's ground covering to be unreinforced concrete at least 100 mm thick "to mix ST 1 in BS 8500".
• AD C, in the floor provision for ground gases, requires concrete to "mix ST2 in BS 8500 or, if there is embedded reinforcement, to mix ST4 in BS 8500".

So the designations ST1, ST2 and ST4 are not trade slang — they are the standardised mixes the approved document points at. If you are building something that has to satisfy building control, the mix is part of the specification, and the mix designation is what the supplier needs.

Why a designated mix is different from a ratio on site

A volumetric mix on site — "1 : 2 : 4" — controls the proportions of the materials you tip into the mixer. A designated mix controls the properties of the concrete: its strength class, its exposure resistance, its maximum water/cement ratio and its cement content. Those are different promises. Two site mixes with the same nominal ratio can land on either side of a strength class depending on the sand, the aggregate and the water, which is why the standards exist.

That has a direct consequence for ordering. A designated mix is specified by the properties you need, and a supplier delivers it to that specification. It is not something a materials calculator can derive from your dimensions, and we do not pretend otherwise.

What this means for a calculation

• The volume is yours to calculate. Your dimensions decide how much concrete is needed — that is what our concrete calculator does.
• The mix is a specification decision. Which designation applies depends on exposure, strength and reinforcement, and it comes from the structural design or the building control submission — not from the volume.
• The dry-materials split is an estimate. The 1.54 bulking allowance and the mix-ratio split on our calculator are planning figures for buying bags. They are not a designated mix, and they do not replace a specification.

Edition status — what the approved document cites, and what is current

An approved document names the edition of a standard that existed when it was written. That edition is not necessarily the current one. The table below sets out, for every standard this page relies on, the title as published, the edition the approved document cites, and the edition BSI catalogues today (22 September 2026). Where the cited edition is withdrawn, the page says so; where we could not confirm the replacement, no current edition is stated.

Source: BSI catalogue records read at knowledge.bsigroup.com on 22 September 2026. Each title, designation, status and date in the last two columns was read from the BSI catalogue page for that standard.

Last verified 22 September 2026. Every requirement quoted on this page was read from the primary source listed below on that date, not from a summary. If a figure could not be confirmed in the primary source it is not on this page.

Where these figures come from

• Approved Document A: Structure, 2013 edition, Section 1 — reference list including BS 8500-1:2006+A1:2012 and BS 8500-2:2006+A1:2012 — GOV.UK publications, "Structure: Approved Document A", checked 22 September 2026.
• Approved Document C: Site preparation and resistance to contaminants and moisture, 2013 edition — paragraph 4.14(a)(i) (mix ST 1 in BS 8500) and the BS EN 206-1 reference in the floor provisions — GOV.UK publications, "Site preparation and resistance to contaminants and moisture: Approved Document C", checked 22 September 2026.
• Approved Document H: Drainage and waste disposal, 2015 edition — reference list including BS EN 206-1 (Method of specifying and guidance for the specifier; Specification for constituent materials and concrete) — GOV.UK publications, "Drainage and waste disposal: Approved Document H", checked 22 September 2026.
• BSI catalogue (“BSI Knowledge”) — product record for each standard listed above: title, current edition and status — knowledge.bsigroup.com, checked 22 September 2026.

Guidance only, not advice

This page is a plain-English summary of published regulations and standards, written to help you plan a job. It is not professional advice, it is not a substitute for the actual document, and it is not a building-control decision.

Building regulations are enforced by your local authority (or an approved inspector) and the facts of a particular job can change the answer. Confirm with your local building control before you start work, and where a job is structural, get it designed by a suitably qualified person. If this page and the source document disagree, the source document wins.