Concrete Slab

Our concrete slab calculator estimates the volume of concrete and the bags of cement, sand and gravel you need for a slab, foundation or footing. Enter the length, width and thickness to get instant material quantities in metric or imperial units.

Common use cases

• Garage and shed floor slabs
• Patio, terrace and driveway pours
• Strip and pad foundations
• Garden paths and concrete pads

How to use this calculator

1. Enter the slab length and width in metres or feet.
2. Enter the slab thickness in centimetres or inches.
3. Press Calculate to see the total concrete volume.
4. Use the bag estimates to plan your cement, sand and gravel purchases.

Example calculation

For a 5 m × 4 m slab at 10 cm thick, you need 2.0 m³ of concrete. That works out to roughly 16 bags of 25 kg cement, 1,100 kg of sand and 1,650 kg of gravel for a standard 1:2:3 mix.

Frequently asked questions

How much concrete do I need for a slab?

Multiply length × width × thickness (in metres) to get cubic metres. A 10 cm slab uses 0.1 m³ per square metre of surface.

How many bags of cement per cubic metre of concrete?

A 1:2:3 mix typically uses around 8 bags of 25 kg cement, 550 kg of sand and 825 kg of gravel per cubic metre.

Should I add extra concrete for waste?

Yes — order 5–10% extra to allow for spillage, uneven sub-base and form deflection.

Can I use this for foundations?

Yes, the same volume formula applies to strip footings, pad foundations and slab-on-grade pours.