How the sheets are counted
The mesh stops short of the formwork on every side, so it covers a slightly smaller rectangle than the slab. Each sheet after the first in a row adds its length less one lap; the same goes for the rows across the slab. The calculator tries the sheets both ways round and keeps whichever takes fewer.
Worked example: a 6 × 3 m slab, SL72
- Mesh area: 6 − 2 × 0.04 = 5.92 m by 3 − 2 × 0.04 = 2.92 m, with the mesh 40 mm inside the formwork.
- Along: 5.92 m fits in one 6 m sheet.
- Across: 2.92 m needs two 2.4 m widths: 1 + (2.92 − 2.4) ÷ (2.4 − 0.225) = 1.24, rounded up to 2.
- Turned the other way, the sheets would take 3 × 1 = 3, so they go lengthwise: 2 sheets, 82 kg of SL72.
- Bar chairs at 800 mm: (8 + 1) × (4 + 1) = 45.
SL mesh sizes
| Mesh | Wire | Mass a sheet |
|---|---|---|
| SL62 | 6 mm | 33 kg |
| SL72 | 6.75 mm | 41 kg |
| SL82 | 7.6 mm | 52 kg |
| SL92 | 8.6 mm | 66 kg |
| SL102 | 9.5 mm | 80 kg |
InfraBuild’s ribbed square mesh, wires at 200 mm centres each way, sheets 6.0 × 2.4 m.
InfraBuild lists an effective area of 5.8 × 2.4 m for each sheet. The calculator laps every edge by 225 mm instead, ends and sides alike, so on a big slab it can come out a sheet or two above a supplier’s count. Set the lap to match your supplier or your plans.
Sydney Reo sells SL72 for driveways, patios, pavements and shed bases. Otherwise the choice belongs to the slab’s design: CCAA asks for the mesh to suit the slab’s thickness and joint spacing.
Laps, cover and bar chairs
- Laps: the two outermost cross wires of each sheet overlap those of the next (NCC Housing Provisions 4.2.11; CCAA). RMIT’s BuildRight guide sets 225 mm as the minimum lap for square mesh.
- Edges: Bunnings cuts the mesh 40 mm smaller than the formwork on each side; CCAA wants 40 mm of concrete at slab edges and joints.
- Height: in driveways and paths, the mesh goes in the top half of the slab with at least 30 mm over it (CCAA). Bunnings’ small slab puts at least 40 mm of concrete over the mesh.
- Bar chairs: no more than 800 mm apart under steel mesh (NCC 4.2.11; CCAA), closer for light mesh such as SL62.
For the concrete itself, the slab calculator works out the cubic metres, the bags and the control joints, and counts the mesh with these same rules.
Follow the plans
House slabs and footings are designed to the NCC or by an engineer, who sets the mesh, the laps and the cover. Use this calculator to count sheets and chairs for the mesh on your plans.
Questions people ask
How many sheets of mesh for a 6 × 3 m slab?
Two 6 × 2.4 m sheets. With the mesh stopped 40 mm short of each edge, it covers 5.92 × 2.92 m: one sheet’s length, and two widths lapped 225 mm. Turned the other way it would take three.
How much should reinforcing mesh overlap?
The NCC’s housing provisions ask for the two outermost cross wires of one sheet to overlap the two outermost cross wires of the next, and CCAA says the same for driveways and paths. RMIT’s BuildRight guide puts the minimum lap for square mesh at 225 mm, the calculator’s starting point.
How far apart should bar chairs be?
No more than 800 mm apart under steel mesh, in both the NCC and CCAA’s data sheet. CCAA adds that light mesh, such as SL62, may need them closer to stop it sagging.
How much does a sheet of SL72 weigh?
InfraBuild lists 41 kg for a 6.0 × 2.4 m sheet of SL72, with 6.75 mm wires. SL62 is 33 kg and SL82 52 kg; the calculator multiplies the sheet count out.
What is the difference between SL72 and SL82?
The wire: 6.75 mm in SL72 and 7.6 mm in SL82, both at 200 mm centres each way, so SL82 carries more steel and weighs 52 kg a sheet against 41. Which one a slab needs is set by its design, so use the mesh on your plans.
Where does the mesh sit in the slab?
In driveways and paths, in the top half of the slab with at least 30 mm of concrete over it and 40 mm at the edges and joints (CCAA). In a house slab the NCC sets the cover: 40 mm to unprotected ground, 30 mm to a membrane in contact with the ground, 20 mm to an internal surface and 40 mm to external exposure.
Sources for the numbers on this page
- InfraBuild — Ribbed square mesh: SL62 to SL102 wire sizes and mass per sheet · checked 4 October 2026
- Sydney Reo Supplies — SL72 reinforcement square mesh, 6.0 m × 2.4 m sheet · checked 4 October 2026
- Australian Building Codes Board — NCC 2022 Housing Provisions, Part 4.2: footings, slabs and associated elements (laps, bar chairs, cover, N20) · checked 4 October 2026
- RMIT University, BuildRight — Concrete slab reinforcement: lapping square mesh (at least 225 mm) · checked 4 October 2026
- Cement Concrete & Aggregates Australia — Residential concrete driveways and paths, data sheet (August 2026, PDF) · checked 4 October 2026
- Bunnings — How to pour a small concrete slab (mesh 40 mm inside the formwork, 40 mm over the mesh) · checked 4 October 2026
Corrections and updates are logged on the sources page.