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Concrete Calculator

Enter the slab dimensions to get cubic metres and an indicative bag count.

Short answer

Volume = length × width × depth (all in metres). A standard 25 kg bag of pre-mixed concrete yields about 0.012 m³, so divide your volume by 0.012 to estimate bags. Always order 5–10% extra for waste.

Slab

m
m
m
%

Fill in the fields above to see your result instantly.

How it works

Volume of a rectangular slab = length × width × depth, all in the same units (we use metres). Add a wastage allowance for spillage and uneven ground.

Worked example

A 4 × 3 m driveway slab 100 mm deep = 4 × 3 × 0.1 = 1.2 m³. With 10% waste: 1.32 m³ ≈ 110 bags of 25 kg pre-mix.

Who should use this

  • •DIY landscaping projects
  • •Estimating before getting a ready-mix quote

Common mistakes

  • ×Mixing units — depth in mm with length in m
  • ×No wastage allowance — concrete spills and surfaces are rarely flat

Frequently asked questions

Should I get bagged or ready-mix?▾

Above ~1 m³, ready-mix is usually cheaper and faster than mixing bags by hand.

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