How much rebar do I need for a 24×24 slab?
A 24 × 24 ft slab with #4 rebar on a 16 in grid takes 76 stock bars of 20 ft, which is 906 linear feet weighing about 605 lb. Tying the grid takes 324 ties and 2 rolls of tie wire, and holding it at mid-slab takes 192 chairs. At 12 in spacing for a driveway it is 101 bars; at 24 in for a light patio, 51.
Rebar for a 24×24 slab by grid spacing
| Grid spacing | 20 ft stock bars (5% extra) | Linear feet | Weight | Ties | Chairs |
|---|---|---|---|---|---|
| 12 in | 101 | 1,208 ft | 807 lb | 576 | 192 |
| 16 in | 76 | 906 ft | 605 lb | 324 | 192 |
| 18 in | 68 | 805 ft | 538 lb | 256 | 192 |
| 24 in | 51 | 604 ft | 403 lb | 144 | 192 |
#4 (1/2 in) rebar with 3 in edge clearance in a 24 × 24 ft slab. Runs longer than 20 ft include a 20 in lap at each splice.
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Rebar or wire mesh for a 24×24 slab?
For a 4 in patio or shed slab, 6 × 6 W1.4 welded wire mesh is usually enough: 13 sheets of 5 × 10 ft, or 1 roll of 5 × 150 ft. Mesh costs less and goes down faster but is hard to keep at mid-depth; it tends to end up on the ground where it does nothing. Rebar on chairs stays where you put it and is the right call for anything a vehicle drives on, a slab over 4 in thick, or a slab on clay or fill. For a garage or driveway, #4 at 12 in is common; for a workshop floor with heavy equipment, step up to #5 at 12 in, which for this slab is 76 bars weighing 961 lb.
Rebar cost and installation for 576 square feet
#4 rebar sells for about $0.70 to $1.00 per foot, or $14 to $20 per 20 ft stick, so the 76 bars for a 16 in grid cost $1,064 to $1,520. Chairs are about 25 cents each ($48) and tie wire a few dollars a roll. A rebar cutter or an angle grinder with a metal wheel handles the cuts; a pigtail tie tool makes the 324 ties go quickly. Keep the grid 3 in from any edge, splice with 20 in laps tied in two places, and stagger the splices. Size the pour itself with the concrete calculator for a 24×24 slab.
Common questions
How many pieces of rebar for a 24x24 slab?
18 bars running the 24 ft direction and 18 running the 24 ft direction at 16 in on center, for 906 linear feet. That cuts from 76 stock bars of 20 ft with 5 percent extra.
How much does rebar for a 24x24 slab weigh?
About 605 lb for #4 bar on a 16 in grid, or 807 lb at 12 in. #4 rebar weighs 0.668 lb per foot.
What spacing should rebar be in a 24x24 slab?
16 in on center for most residential slabs, 12 in for driveways and anything carrying vehicles, and 18 to 24 in for light-duty patios where wire mesh would otherwise be used. Keep it at mid-depth on chairs.