▣ CALCULATORS Updated July 25, 2026
Concrete Calculator
Slab dimensions in, cubic metres and bag counts out.
Length (m)
Width (m)
Depth (cm)
Waste allowance (%)
Result
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How it works
Volume is length times width times depth in metres; the tool adds a waste allowance, converts to cubic yards, and estimates bag count using a typical density of 2400 kg per cubic metre.
Frequently asked questions
How many bags per cubic metre?
A 40 kg bag of premix yields roughly 0.017 m3, so a cubic metre needs about 60 bags — ready-mix is cheaper past 1 m3.
What depth should a slab be?
Garden paths are typically 75-100 mm; driveways and load-bearing slabs usually need 100-150 mm with reinforcement.
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