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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

Length

Width

Depth

Wastage allowance

Fill in the fields above to see your result instantly.

Calculation method, coverage and version

Inputs used: Length, Width, Depth, Wastage allowance.
Calculation approach: The calculator applies the rules and assumptions described in “How it works” to the values you enter. Rounding can cause small differences from an official or provider calculation.
Coverage: Utility. UK nations, tax treatment, local rules and provider criteria can differ; check the official sources shown below before acting.
Content version: No page-specific review date is currently published. Treat the result as indicative and verify current rules independently.

Not included unless explicitly requested: personal circumstances not entered, provider discretion, future rule changes, professional fees and case-specific exceptions. Read the full calculator methodology.

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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