Concrete Calculator
Calculate concrete volume in cubic metres or yards for slabs, footings, and posts. Supports metric and imperial units with bag count and waste factor.
Results
How to Calculate Concrete
Multiply length x width x depth to get volume. In metric, this gives cubic metres directly. In imperial, you get cubic feet — divide by 27 to convert to cubic yards. One cubic yard (0.76 m³) fills roughly 7.4 square metres (80 sq ft) at 100 mm thick.
For premix bags, divide total volume by the yield per bag (check the packaging — it varies by brand and region). Always round up and add 5-10% for waste due to uneven ground and spillage.
Concrete Thickness Guide
The right slab thickness depends on load. Footpaths and patios: 100 mm (4 in). Residential driveways: 125-150 mm (5-6 in). Garage floors and heavy vehicle areas: 150-200 mm (6-8 in) with mesh or rebar reinforcement. Always confirm minimum thickness with your local building authority.
Frequently Asked Questions
How much concrete do I need for a 3x3 metre (10x10 ft) slab?
A 3x3 m slab at 100 mm thick requires about 0.9 cubic metres (1.2 cubic yards) of concrete. In premix bags, that's roughly 56 bags at 80 lb (36 kg) or about 36 bags at 20 kg, depending on your region.
How thick should a concrete slab be?
Patios and walkways: 100 mm (4 in). Residential driveways: 125-150 mm (5-6 in). Heavy-duty pads, garages, or shop floors: 150-200 mm (6-8 in). Always check your local building regulations for minimum requirements.
Should I add extra concrete for waste?
Yes. Standard practice is to order 5-10% extra to account for uneven subgrade, spillage, and over-excavation. This calculator includes a waste factor option.
What's the difference between premix bags and ready-mix delivery?
Premix bags (20-40 kg / 40-80 lb) are practical for small projects under 0.5 m³. For larger pours, ready-mix truck delivery is faster, stronger (consistent mix), and usually cheaper per cubic metre.