Rebar calculator
Enter the slab size, grid spacing and how far the bars stop short of the edges. The calculator lays out the grid both directions.
Rebar to buy
11 20 ft bars
- Linear feet
- 190 ft before extra
- Bars running lengthwise
- 10 at 9.5 ft
- Bars running widthwise
- 10 at 9.5 ft
- Grid intersections to tie
- 100 ties
How it works
The bars stop short of each edge by the clearance you enter, so concrete fully covers them. The calculator counts how many bars fit across the slab at your spacing (in both directions), multiplies by each bar’s length, and divides the total by your stock bar length. The extra percentage covers overlaps where bars are spliced and cutting waste.
Example
With slab length 10 ft, slab width 10 ft, grid spacing 12 in, edge clearance 3 in, bar length: 20 ft bars, extra for laps and cuts 10%, the answer is 11 20 ft bars.
Tips before you buy
- Support rebar on chairs or blocks so it sits in the middle of the slab, not on the ground.
- Where bars splice, overlap them generously and tie them together. Your plans or local code set the exact lap length.
- Many residential slabs use #3 or #4 bar on a 12 to 18 inch grid, but follow your plans or engineer.
Common questions
How much rebar for a 10×10 slab?
On a 12 inch grid with 3 inches of edge clearance, 10 bars each way at 9.5 feet, or 190 linear feet. That’s 11 bars of 20 ft stock with 10% extra.
How far apart should rebar be in a slab?
12 to 18 inches each way is common for residential slabs. Your plans or local code have the final say.
How far from the edge should rebar stop?
Typically about 2 to 3 inches, so the steel is fully covered by concrete.