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Concrete calculator

Work out the volume of concrete and number of bags for a slab or foundation.

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Enter Length (m), Width (m), Thickness (cm) and the Concrete calculator works out Concrete volume (m³), Approx. weight (kg), 25 kg premix bags straight away. For instance, with Length (m) = 5, Width (m) = 4 and Thickness (cm) = 12 it returns Concrete volume (m³) = 2.4, Approx. weight (kg) = 5,760 and 25 kg premix bags = 209.

How to use it

  1. Enter your values: Length (m), Width (m), Thickness (cm).
  2. Read the result instantly: Concrete volume (m³), Approx. weight (kg), 25 kg premix bags.

Frequently asked questions

How does the Concrete calculator work?

It takes Length (m), Width (m) and Thickness (cm) and derives Concrete volume (m³), Approx. weight (kg) and 25 kg premix bags from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

3 values: Length (m), Width (m) and Thickness (cm). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Length (m) = 5, Width (m) = 4 and Thickness (cm) = 12, the calculator returns Concrete volume (m³) = 2.4, Approx. weight (kg) = 5,760 and 25 kg premix bags = 209. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

How much does the result change with different inputs?

It moves a lot. Using Length (m) = 6, Width (m) = 4 and Thickness (cm) = 13 instead, Concrete volume (m³) goes from 2.4 to 3.12 — which is why it is worth testing a few scenarios rather than trusting a single figure.

What does it give for smaller values?

Scaled down to Length (m) = 5, Width (m) = 4 and Thickness (cm) = 11, Concrete volume (m³) comes out at 2.2. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Buying the right amount at the merchant: how many tiles, how much paint, how many bags of concrete, and what it all comes to.

What is the most common mistake?

Ordering the exact calculated quantity. Cuts, breakage and pattern matching mean tiles need 10% spare and more on a diagonal layout — and a second batch rarely matches the first for colour.

How accurate is it, and what are the limits?

Estimate only — confirm quantities with your supplier.

What is the difference between the Concrete calculator and the Post Hole Concrete Calculator?

This one returns Concrete volume (m³) and Approx. weight (kg); the Post Hole Concrete Calculator returns Concrete per hole and Bags needed (20 kg). That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Concrete blocks calculator is the closest one after this: Estimate the number of concrete blocks needed to build a wall.

Further reading

All guides →
How-toHow Much Concrete Do You Need?Concrete is measured by volume: length × width × depth. Here's how to work out cubic metres, add for waste, and choose bags or ready-mix.How-toHow Many Concrete Blocks Do I Need? Blocks, Mortar and WasteWork out how many concrete blocks a wall needs from its area, add mortar and a waste allowance, and avoid a second trip to the yard.How-toHow Much Gravel Do I Need?Multiply area by depth for a volume, then convert to weight — gravel is about 1.5 tonnes per cubic metre. Here's the method, depths by job, and how to order.How-toHow to Measure Roof PitchRoof pitch is rise over run, like 6:12. Here's how to measure it with a level, how to convert it to an angle or percentage, and why it matters.GuideMaterials for a Retaining Wall — And the Thing That Actually Makes Them Fall OverBlocks, base gravel, drainage stone, geogrid and pipe, counted from the calculator's own output. Then the number nobody puts in a materials list: a saturated backfill pushes about 2.2 times as hard as a drained one.GuideHow Much Rebar a Slab or Wall Needs — Bars, Laps and CoverBars each way, splice lengths in bar diameters, cover from the edge, and the exact tonnage to order. Run against the calculator, including the two places where its bar count comes out short.