Reviewed, sourced guidance

How this calculator works and where it stops

Published 23 Sept 2026Reviewed 27 Sept 20262 min read

Direct answer

Plan dimensions and depths accept metres, centimetres or millimetres. Dimensions convert to metres and depths to millimetres; each component volume is multiplied by its integer count before waste and any product-specific bag estimate are calculated.

This page exists so the calculation can be checked rather than trusted. It states the formula, the assumptions and their version, and the limits of the result.

Key takeaways

Convert plan dimensions and depths to metric units; multiply each supported area by its depth and count.
Enter an allowance from 0 to 50 per cent; no default is assumed.
Bag counts use a cited product yield or a value entered from the selected product data.
Assumption version 2026-09-27-v1 is reported with every result.
The calculator returns no price.

Evidence note

Source-led homeowner information with its scope, limits and commercial status recorded.

View the full evidence note

Produced by: My Concrete Calculator
Jurisdiction: Applies to work in the United Kingdom; specification requirements vary across England, Wales, Scotland and Northern Ireland
Page scope: The method, assumptions and limits behind the quantity estimates on this site.
Default subject: Concrete quantity estimation for slabs, footings and similar straightforward pours, including waste allowances and optional product-specific bag estimates.
Excludes: Structural, engineering or specification advice; Mix design or strength class selection for any specific job; Prices, quotations or supplier comparisons; Supplier recommendation, ranking or referral; Concrete supply, delivery, placing or finishing
Published: 2026-09-23
Reviewed: 2026-09-27
Commercial status: Information publisher only. No supplier is active, no lead capture runs, no enquiries are collected and no affiliate links are present.

The assumptions are versioned and expected to change as better sources are found. Each result reports the version it was produced under.

How this guidance is produced · Correction submission status

Source review cadence

Every source cited on this site carries a dated check and a recheck trigger, so stale evidence is replaced rather than quietly relied on.

Source	Last checked	Recheck	Triggers an early review
MyJobQuote new driveway cost guide, UK 2026 prices (observed 2026-09-25)	2026-09-25	every 45 days	Price guide date, range or inclusions change; Cost wording on this site changes
GOV.UK, Structure: Approved Document A, Building Regulations 2010 (observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
legislation.gov.uk, Building Regulations 2010, Schedule 1 Part A Structure (observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
The Concrete Centre, Standards for concrete: BS 8500 (observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
The Concrete Centre, BS 8500 for building and civil structures (2024 guide to BS 8500:2023; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
The Concrete Society, Principles of mix design (published 2025-06-03; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
BRMCA, Ready-Mixed Concrete practical guide for site personnel (July 2020; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
Heidelberg Materials, Merchant concrete guide (December 2025; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
Tarmac, Blue Circle Multi-Purpose Concrete product data sheet (December 2023; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
Heidelberg Materials, 40N Concrete technical data sheet (July 2025; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
The Concrete Society, Estimation of concrete volume requirement (published 2025-06-03; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
The Concrete Society, Curing concrete (published 2025-06-03; observed 2026-09-25)	2026-09-25	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes
NHBC Standards, 2026 edition and applicability (observed 2026-09-24)	2026-09-24	every 120 days	Cited page, standard edition or regulation changes; A claim tied to this source changes

The formula

Plan dimensions are converted from metres, centimetres or millimetres to metres; depths are normalized to millimetres and divided by 1000. Each row repeats one supported area and depth by its integer count; counts range from 1 to 1,000. Row and repeated areas must be non-overlapping, which the estimator cannot check.

The waste allowance is applied as a percentage increase to the net volume, and bag counts are rounded up because whole bags are what you can buy.

row volume = component area x (component depth in millimetres / 1000) x count
net volume = sum of the component volumes
volume with waste = volume x (1 + waste percent / 100)
bags = volume with waste / selected bag yield, rounded up

The assumptions

Every number the calculator assumes rather than computes is listed here, so a disagreement can be traced to a specific figure.

Bag yields differ by product. These examples are planning quantities; check the selected product packaging and project specification.

Blue Circle Multi-Purpose Concrete, 20 kg: approximately 0.010 cubic metres per bag.
Heidelberg Materials 40N Concrete MaxiPack20: approximately 0.008 cubic metres per bag.
No bag count is returned until a product yield is selected or entered.
No waste allowance is assumed; enter a supplier or job-specific value from 0 to 50 per cent.
The Concrete Society gives a general overage guide of 5 per cent for formed elements and 10 to 15 per cent for unformed elements.
Supplier minimum loads and charges are not assumed; check the selected supplier terms.

Sources for this section: Tarmac, Blue Circle Multi-Purpose Concrete product data sheet (December 2023; observed 2026-09-25)Heidelberg Materials, 40N Concrete technical data sheet (July 2025; observed 2026-09-25)The Concrete Society, Estimation of concrete volume requirement (published 2025-06-03; observed 2026-09-25)

What this tool does not do

It does not choose a depth or a mix class, because both depend on information it does not have.

It does not return a price: mix, quantity, delivery and site conditions vary, and this preview has no comparable supplier-price dataset.

No structural or engineering advice.
No mix design or strength class recommendation.
No supplier recommendation, ranking or referral.
No price, quote or estimate of cost.

Next steps

Check the assumptions version on any result you rely on.
No correction submission route is active in this preview; use the cited source and displayed version to check an estimate.