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Reinforcing a concrete slab with rebar means laying a grid pattern in both directions at a specified spacing — figuring out exactly how many runs and how much total rebar that grid needs is easy to miscount by hand. This calculator finds the number of rebar runs in each direction and the total rebar length needed for a slab, based on its dimensions and grid spacing.
How it works
Enter the slab's length and width, and the grid spacing between rebar runs. The calculator finds how many runs fit across each direction, then adds up the total length of rebar needed for the full grid.
- Enter slab length (ft).
- Enter slab width (ft).
- Enter grid spacing (in).
- Click Calculate to see your results.
Examples
A 20x10 ft slab at 12" spacing
This needs 21 runs one way and 11 runs the other, totaling 430 feet of rebar for the full grid.
Who should use it
- Estimating rebar material needs for a concrete slab or footing project.
- Planning a rebar grid layout before pouring concrete.
Industry applications
- Residential and commercial concrete construction
- DIY patio, driveway, and foundation projects
Advantages
- Calculates the exact run count in both directions plus total rebar length.
- Works for any rectangular slab dimensions and spacing.
Limitations
- Does not add extra length for splice overlaps between shorter rebar sections.
Common mistakes to avoid
- Forgetting to add extra rebar length for splice overlaps when pieces are shorter than the slab dimension.
- Using a spacing wider than local code requires for the slab's intended load.
Best practices
- Always confirm the required rebar spacing and grade with local building code or a structural engineer before finalizing a slab design — this calculator handles the geometry, not the engineering specification.
Tips
- Order a bit more rebar than the calculated total to account for splices and any cutting waste.