The job
Modelled, not recorded. Every figure here is the answer the Welded Wire Mesh Calculator — Reinforcing Mesh Sheets for a Slab gives for these inputs, written down in both unit systems and re-run whenever the site is built. No job was carried out, so there is no measured overrun on this page.
The slab is the base of a single prefabricated or block-built garage, 6 m (19.69 ft) long and 4 m (13.12 ft) wide. The drawing calls for one layer of welded steel fabric, laid on spacers so it sits in the slab, stopping 50 mm short of each edge so the concrete covers its cut ends.
The sheet is 4.8 x 2.4 m, the UK standard sheet (BS 4483 fabric), the standard size British fabric is sold in. The calculator does not need the grade, which is the drawing's choice: the bars' size and spacing change the weight of a sheet, not the number of them.
The lap between sheets, 202 mm, and the end overhangs, 152 mm, stay at the calculator's figures, which come from the US Wire Reinforcement Institute's manual it cites. A British specification may set its own lap for the grade of fabric, and if it does, that figure goes into the lap input before the count is trusted.
The inputs, exactly as entered
| Input | Value | Why |
|---|---|---|
| Slab Length | 6 m (19.69 ft) | The garage base's long side, outside of the formwork. |
| Slab Width | 4 m (13.12 ft) | The short side, measured the same way. |
| Gap Between the Slab Edge and the Mesh | 50 mm (1.97 in) | The gap left between the mesh and the slab edge on every side, so the cut ends are buried in concrete. |
| Sheet As Sold | 4.8 x 2.4 m, the UK standard sheet (BS 4483 fabric) (4.8 x 2.4 m (15.7 x 7.9 ft), the UK standard sheet) | The standard British sheet, chosen from the calculator's list so its size is exact. |
| Lap Between Sheets, Wire to Wire | 202 mm (7.95 in) | Left at the calculator's own default. |
| End Overhangs of One Sheet, Both Together | 152 mm (5.98 in) | Left at the calculator's own default. |
The working, step by step
1. Slab area the mesh covers
23.01 m² (247.7 sq ft)
The slab less the edge gap on every side leaves 23.01 m² for the mesh to cover. It is smaller than the slab itself, and on a small base the gap is a noticeable share of it.
2. Sheets with their length along the slab
4 sheets
The calculator first lays every sheet with its long side along the slab, laps and all, and counts 4 sheets. That orientation suits a long narrow slab; on a base this wide it leaves a strip to cover with cut sheets.
3. Sheets with their length across the slab
3 sheets
Then it turns the sheets through a right angle, long side across the slab, and counts 3 sheets. Here one sheet spans the whole width, so this is the layout it keeps: the fewer sheets of the two.
4. Sheets in each run, in the layout used
3 sheets
In that layout the sheets lie side by side along the slab, overlapping at each joint: 3 sheets make one run from end to end, and 1 such run covers the width.
5. Sheets that need cutting, in the layout used
3 sheets
Every sheet is longer than the base is wide, so all 3 are trimmed to length on site with bolt cutters or a disc. The offcuts are strips too narrow to use elsewhere on this slab, which is why the area bought is larger than the area covered.
6. Area of the sheets bought
34.56 m² (372 sq ft)
The sheets bought cover 34.56 m², against the 23.01 m² they reinforce. The difference is the laps and the trimmed ends, the real cost of a sheet product on a small slab.
Mesh sheets to order
3 sheets
Order 3 sheets of fabric in the grade the drawing names, and spacers to hold it at the cover depth the specification gives. A sheet of the standard size is heavy and awkward for one person, so plan the lift and the cutting before the delivery. The count is the sheets to place, not a design: whether the base needs mesh at all, and which grade, is for the specification and for whoever designs the slab.
What to buy
| Quantity | Figure | What it is for |
|---|---|---|
| Mesh sheets to order | 3 sheets | Standard sheets of welded steel fabric in the grade the drawing specifies. |
The allowance, and what it does here
There is no percentage on this calculator: the sheets are counted in a layout, so the laps and the cut ends are already in the count. What the layout cannot see is a sheet damaged in delivery or a slab with a step or an inspection chamber in it, where a sheet is cut around an opening and the offcut is lost. On a simple rectangular base, the layout count is the order.
The common mistake
Dividing the slab area by the area of a sheet
On this base the area divided by one sheet, rounded up, happens to give the right count, and that is luck. On the longer garage in the section below the same division still says the same number, while the layout needs one more sheet, because sheets cannot be stretched: they lap where they meet, they come in one size and one shape, and the strips left over after cutting are too narrow to fill a gap elsewhere. Count the layout, sheet by sheet, as the calculator does, and buy the whole sheets it finds.
Change the job, and see what moves
A longer garage on the same plan
Slab Length: 7.5 m (24.61 ft) → 4 sheets
Make the garage 7.5 m long instead and the order rises to 4 sheets. The calculator now finds a different layout cheaper: 2 runs side by side of 2 sheets each, which is the kind of switch that is hard to see without counting both ways.
The same base, with the mesh taken to the edge
Gap Between the Slab Edge and the Mesh: 0 mm (0 in) → 3 sheets
Take the mesh right to the edge and the count stays at 3 sheets, although the area covered grows to 24 m². The edge gap changes the area, not the layout, on a slab this size; it matters for the steel's protection, not for the order.
What to run next
- Concrete Calculator
The same base's length, width and thickness give the concrete the mesh is cast in.
- Rebar Chair and Bolster Count Calculator
The mesh is held up on spacers or chairs, counted from the slab area and a spacing.
- Rebar Calculator
If the drawing calls for bar instead of fabric, or bar at the edges, it is counted on a grid by this calculator.
Sources
The method and every constant behind these figures belong to the Welded Wire Mesh Calculator — Reinforcing Mesh Sheets for a Slab, version 1.0.0, last verified 2026-10-05. It rests on:
- Wire Reinforcement Institute, Manual of Standard Practice — Structural Welded Wire Reinforcement (WWR-500, 7th edition, © July 2006): style designation (6 x 12-W12 x W5 means wires at 6 in and 12 in, W12 and W5 being 0.12 and 0.05 sq in); width the centre-to-centre distance between the outside longitudinal wires, not including overhangs; side overhangs no greater than 1 in (25 mm) a side where none is specified; length tip to tip, always including the end overhangs; preferably the sum of the two end overhangs should equal the transverse wire spacing; common sheet sizes 96 in x 12.5 ft (US except west coast), 96 x 16, 96 x 20, 84 x 20 and 84 x 25 ft (US west coast), and 48 in x 8 ft and 96 in x 12, 14, 16 and 20 ft in Canada (2438 mm x 3.7, 4.3, 4.9 and 6.1 m); styles may be obtained in roll form, flattened and cut to size before placement; plain wire splices not less than one space + 2 in (50 mm) nor 6 in (150 mm), overhangs added to the splice length; for slabs on ground the minimum splice is 2 in plus overhangs
- American Society of Concrete Contractors, "WWR Lap Splice Requirements": ACI 439.5R-18, Guide for Specification, Manufacture and Construction Use of Welded Wire Reinforcement, section 6.4, gives a lap splice of one square plus 2 inches for plain wire WWR; non-structural slabs-on-ground are designed to ACI 360 and the design professional sets the splice
- BSI, BS 4483:2025 Steel fabric for the reinforcement of concrete. Specification (current; published 27 March 2025; supersedes BS 4483:2005, which is withdrawn), the standard UK fabric is made to: sheets of machine-welded fabric made from ribbed bars
- Capital Reinforcing (Ireland) Ltd, reinforcing mesh product page: mesh produced to BS 4483; A type square mesh A393, A252, A193 and A142, in standard sheets or flying end sheets
- Heaton Manufacturing, Steel Reinforcing Mesh Sizes (size chart, reviewed 3 April 2026): steel reinforcing mesh sizes in the UK are defined by BS 4483 and commonly supplied in standard 4.8 m x 2.4 m sheets, area 11.52 m²; A393, A252, A193 and A142 at a 200 mm pitch both ways
- Jewson, BRC Standard Fabric Reinforcement 4.8 x 2.4m x 6mm (L x W x Dia): the maker's part WWS A142, product length 4.8 m, product width 2.4 m
Frequently asked questions
- How many mesh sheets for a 6 by 4 m garage base?
- In the UK standard sheet, with a 50 mm edge gap and the calculator's lap, 3 sheets, laid with their long side across the base and trimmed to fit.
- Why can't I just divide the slab area by the sheet area?
- Because sheets lap where they meet and are trimmed at the edges. Here the sheets bought cover 34.56 m² to reinforce 23.01 m².
- Does the grade of mesh change the number of sheets?
- No. The grade changes the bars in each sheet and its weight; the sheet size, and so the layout and count, is the same.