Know what to buy, and what it will cost

Material calculators that finish the job: quantity, purchase units, waste allowance and a price you can take to the merchant.

Example: a 10 × 10 ft slab at 4 in — change any figure to make it yours.

Shape
Units

Why 10%?

Concrete goes missing between the mixer and the form. The subgrade is never perfectly flat, edges over-excavate, some spills off the barrow and some stays in the drum. 10% is the standard trade allowance for a slab on reasonably level ground. Increase it on rough or sloping ground.

Add a price

Prices vary by region and month, so nothing is filled in for you.

Material estimate

10 ft × 10 ft × 4 in · 10% waste

1.36

Cubic yards

You need to buy

62 × 80 lb bags
or 82 × 60 lb bags
or 98 × 50 lb bags
or 123 × 40 lb bags
or 55 × 90 lb bags
Open the full concrete slab calculator

Every calculator

12 tools across 5 categories. Each one gives you quantities, purchase units and a cost.

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How we calculate

Every figure comes from a manufacturer data sheet or a published trade standard, cited on the page that uses it. Purchase quantities always round up, because you cannot buy part of a bag. Where a material's density genuinely varies by supplier, the range is shown rather than quietly averaged.

Read the methodology