A 12×12 slab with a 12 in grid of #4 bars and 3 in of edge cover. Change the spacing and bar size to match your plans.
How it works
Bars each way = (slab size − 2 × cover) ÷ spacing + 1. Each bar runs the slab less the cover; bars longer than the stock length get a lap of 40 bar diameters by default.
Example: a 12×12 ft slab with #4 bars 12 in apart and 3 in edge cover needs 12 + 12 bars, 276 ft of rebar (24 × 20 ft bars) weighing 184 lb.
At a glance
Same settings as the calculator above, changing only the spacing.
| Spacing | Rebar | 20 ft bars | Weight |
|---|---|---|---|
| 12 in | 276 ft | 24 | 184 lb |
| 16 in | 207 ft | 18 | 138 lb |
| 18 in | 184 ft | 16 | 123 lb |
| 24 in | 138 ft | 12 | 92 lb |
Rebar sizes (ASTM A615)
| Bar | Diameter | Weight per ft | 20 ft bar |
|---|---|---|---|
| #3 | 0.375 in | 0.376 lb | 7.52 lb |
| #4 | 0.5 in | 0.668 lb | 13.36 lb |
| #5 | 0.625 in | 1.043 lb | 20.86 lb |
| #6 | 0.75 in | 1.502 lb | 30.04 lb |
| #7 | 0.875 in | 2.044 lb | 40.88 lb |
| #8 | 1 in | 2.67 lb | 53.40 lb |
Common questions
How far apart should rebar be in a slab?
Residential slabs commonly use #3 or #4 bars 12 to 18 inches apart each way, but the spacing should come from your plans or local code.
How much do rebar laps need to be?
Lap length depends on bar size, concrete strength and code. 40 bar diameters is a common rule of thumb: 20 in for #4 bar. Check your plans.
How heavy is rebar?
#3 weighs 0.376 lb/ft, #4 0.668 lb/ft, #5 1.043 lb/ft and #6 1.502 lb/ft under ASTM A615.
Sources
- ASTM A615 bar sizes and weights: https://www.astm.org/a0615_a0615m-22.html