Concrete calculator
Enter the slab size and thickness. You’ll get cubic metres for a ready-mix order and a bag count if you’re mixing it yourself.
Measuring in feet and inches? Use the US version
Concrete needed
0.99 cubic metres (m³)
- Bags of ready-mix
- 99 bags
- Litres
- 990 L
- Area
- 9 m²
How it works
Volume is length × width × thickness, with the thickness converted from millimetres to metres. The calculator adds your extra percentage. The bag count divides the volume in litres by the yield printed on the bag.
Example
With slab length 3 m, slab width 3 m, thickness 100 mm, extra for spillage and uneven ground 10%, yield per bag 10 litres, the answer is 0.99 cubic metres (m³).
Tips before you buy
- 100 mm is a common thickness for paths and shed bases. Driveways and bases for heavy loads are thicker.
- Above about half a cubic metre, mixing bags by hand is hard work. Compare the cost of ready-mix or a mix-on-site delivery.
- Check local rules before you pour. Some bases near boundaries or buildings need approval.
Common questions
How many bags of concrete are in a cubic metre?
About 100 bags if each makes 10 litres, which is typical for a 20 kg bag.
How much concrete for a 3 × 3 m shed base?
At 100 mm thick, 0.9 m³, or 0.99 m³ with 10% extra.
How thick should a concrete shed base be?
About 100 mm on a compacted sub-base is typical for a garden shed.