Two-way grid with edge cover — diagram updates as you type
Typical starting points for concrete slab rebar spacing—verify with engineering.
| Project | Typical Thickness | Common Bar | Typical Spacing |
|---|---|---|---|
| Garage Slab | 5–6 in | #4 – #5 | 12 in OC each way |
| Driveway | 5–6 in | #4 | 12–16 in OC |
| Patio Slab | 4 in | #3 – #4 | 16–18 in OC |
| Sidewalk | 4 in | #3 or mesh | 18 in OC or mesh |
| Strip Footing | 8–12 in deep | #4 – #5 | 12 in OC |
Pre-fill the rebar grid spacing calculator for common flatwork.
24×24 ft, #4 at 12 in OC, 2 in cover.
12×12 ft, #3 at 18 in OC, 1.5 in cover.
20×40 ft, #4 at 12 in OC, 2 in cover.
4×50 ft, #3 at 18 in OC, 1.5 in cover.
This reinforcement spacing calculator builds a two-way grid: bars running lengthwise and widthwise across the effective area inside cover. Total steel length is the sum of both directions before waste and weight.
Pair results with the rebar calculator for footing and wall modes, and the rebar weight calculator when you already know stick counts.
Center of one bar to center of the next is 12 inches. The clear gap is slightly less than 12 inches because bar diameter takes space.
Many specs use 1.5 to 2 inches bottom and side cover for slabs on grade. Enter what your drawing shows.
The dashed line is the effective reinforcement zone after subtracting edge cover from the slab footprint.
This tool models a two-way grid typical for slabs. For single-direction steel, count one direction manually or use wall/column modes on the main rebar calculator.
Weight is included using standard lb/ft by bar size. For mixed sizes, run each schedule line separately on the weight calculator page.
Light residential patios often use #3 or #4 at 18 in OC when engineering allows. Heavier use or poor soil may require tighter spacing.