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Concrete Calculator

Calculate concrete volume for slabs, footings and columns, plus how many bags to buy. Metric and imperial.

Project shape

Pick a shape, enter dimensions, get volume and bags.

Concrete needed
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Enter your dimensions.

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How the volume is computed

Slabs and footings use length times width times thickness; round columns use pi times radius squared times height. Imperial inputs are converted to cubic meters internally, and the result is shown in both cubic meters and cubic yards since suppliers quote either unit.

Bags and waste allowance

Bags are counted by dividing the total volume by the yield of your chosen bag size, always rounding up. The 10% waste allowance covers spillage, uneven ground and formwork gaps; keep it on unless your measurements are exact and the site is clean.

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Concrete Calculator FAQs

How thick should a concrete slab be?
4 inches (0.1 m) suits foot traffic like patios; 6 inches (0.15 m) handles cars and light trucks. Going thicker than needed mostly adds cost, not strength.
Why add 10% extra concrete?
Forms leak, subgrades are never perfectly level, and spillage happens. Ordering exactly the calculated volume is the most common cause of coming up short mid-pour.
Can I mix bags instead of ordering ready-mix?
For jobs under about 1 cubic meter, bags are practical. Larger pours set faster than you can mix by hand, so ready-mix delivery is safer and often cheaper per unit.
How long does concrete take to cure?
It is walkable in 24-48 hours but reaches full strength around 28 days. Keep it damp for the first week for the strongest cure.
What if my slab is an L-shape?
Split it into rectangles, calculate each with the slab mode, and add the volumes together. The same trick works for any irregular footprint.
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