Rebar and wire mesh for a concrete slab
A 20×20 ft slab on an 18 in grid needs 574 ft of #4 rebar, which is 29 bars at 20 ft, plus 45 chairs. Placed, that runs $766 – $1,276. Wire mesh for the same slab is 9 sheets, about $255 – $425 placed.
#4 rebar, 18 in grid
574 ft
29 bars at 20 ft, and 45 chairs for a 20×20 ft slab. Installed: $766 – $1,276.
- Rebar materials
- $588
- Wire mesh instead
- 9 sheets, 5×10 ft
- Mesh materials
- $177
- Mesh installed
- $255 – $425
An estimate, not a bid. A contractor's price depends on your site, access and timing.
National prices, estimated. Rebar, mesh and chair prices are our own assumptions until a supplier survey exists; the quantities depend only on your inputs.
Contractor? Put the steel on a branded estimate next to the concrete and labor.
Rebar and mesh by slab size
#4 rebar on an 18 in grid with 20 in splice laps; mesh in 5×10 ft sheets with overlap. Installed prices are national.
How much rebar for a concrete slab
Rebar runs both ways in a grid. Count the bars across each direction (the side length divided by the spacing, plus one) and multiply by the length they span. Where a run is longer than a 20 ft stock bar, two bars overlap by a lap of 40 bar diameters, which is 20 in for #4. Tightening the grid from 18 in to 12 in takes the 20×20 slab from 574 ft to 840 ft.
The bars have to sit in the middle of the slab, not on the ground, so they go on chairs, roughly one every 3 ft each way. Tie the crossings with wire so the grid does not shift during the pour.
Wire mesh for a concrete slab
Welded wire mesh comes in flat sheets or rolls; the calculator uses 5×10 ft sheets. Overlap each sheet by one grid square at the edges, which adds about 10% to the area, and lift it on chairs too. Mesh left lying on the gravel does nothing once the concrete is poured over it.
Concrete slab reinforcement: rebar, mesh or none
Mesh holds shrinkage cracks tight on patios, walks and shed pads. Rebar adds real strength, which matters under vehicles, heavy loads or on soft ground. Our slab prices assume mesh below 500 sq ft and rebar from 500 sq ft up; for the 20×20 example rebar costs $681 more than mesh at the midpoint. The concrete slab cost calculator prices the whole pour with either one.