Use the pour calculator in the docket above: enter the length and width in metres and the thickness in millimetres for each slab, footing or path. The totals update as you type and go into your quote request if you send it.
How the concrete slab calculator works
Concrete is ordered by volume, in cubic metres (m³). The calculator in the pour docket above multiplies the length and width of each pour, in metres, by its thickness in millimetres, then adds the rows together. You can list several pours on one docket: the house floor, the garage, the footings and a path. It shows the total area in square metres, the net volume and how many 6 m³ ready-mix trucks the job needs, with about 7% extra for waste.
The formula is simple: volume (m³) = length (m) × width (m) × thickness (mm) ÷ 1,000. A 10 m by 8 m house floor at 100 mm is 10 × 8 × 0.1 = 8 m³, which is two trucks once you allow for waste. For strip footings, use the trench length, the footing width and its depth.
Typical concrete slab thickness and strength
These are common starting points for South African work. Your plans, an engineer's design or the NHBRC requirements always take priority.
| Job | Thickness | Strength |
|---|---|---|
| Garden path, tank stand, braai area | 75–100 mm | 15–20 MPa |
| House floor (surface bed) | 100 mm | 20–25 MPa |
| Garage floor, carport, driveway | 100–150 mm | 25–30 MPa |
| Strip footings for a single-storey house | 200–300 mm deep, about 600 mm wide | 20–25 MPa |
| Rib-and-block topping | 50 mm over the blocks | 25–30 MPa |
| Suspended or roof slab | 150–250 mm, engineer designed | 25–35 MPa |
| Warehouse or workshop floor | 150–200 mm, engineer designed | 30–35 MPa |
Why order more than the calculator says
Ground is never perfectly level, shutters bow a little and some concrete stays in the truck, the pump line or the wheelbarrow. Contractors usually order 5 to 10% more than the net volume. Running short halfway through a pour leaves a cold joint, which is a weak point, so a little extra is cheaper than a second delivery. For pours under about 1 m³, site-mixed concrete from cement, sand and stone is often more practical than a part load of ready-mix.
From the calculator to a concrete slab price per m²
People often ask for a concrete slab price per m², but the volume is only part of it. The rate depends on the thickness, the strength class, the reinforcing mesh or rebar, the damp-proof membrane, excavation and sub-base compaction, shuttering, pumping, labour, finishing and travel. Send your totals with the quote form, and a contractor or supplier near you will price the whole job. Read more in our concrete slabs guide and the ready-mix concrete guide.