Enter slab dimensions and grid spacing to find how many rebar bars you need and total linear feet for your concrete slab.
Estimates only.
The calculator places bars across the width at the specified spacing, plus one bar at each edge. Bars run lengthwise are spaced across the slab width the same way. Total linear feet equals bars running along the length (each as long as the slab length) plus bars running across (each as long as the slab width). Divide by 20 and round up to get the number of standard 20-foot rebar sticks.
Decide on your grid spacing (12 inches is typical for residential slabs). Divide the slab width in inches by the spacing and add 1 to get bars running lengthwise. Do the same for the slab length to get bars running widthwise. Multiply each group by slab dimension to get linear feet.
Residential driveways and patios typically use #3 rebar (3/8 inch diameter) on 18-inch centers or #4 rebar (1/2 inch) on 12-inch centers. Structural slabs and footings often specify #4 or #5 rebar. Always follow your local building code or engineer specifications.
#3 rebar runs roughly $0.30 to $0.50 per linear foot; #4 rebar runs $0.45 to $0.70 per linear foot depending on region and current steel prices. Prices fluctuate with steel markets, so get a current quote from your supplier.
Rebar should sit in the lower third of the slab, typically 1.5 to 2 inches from the bottom for a 4-inch slab. Use rebar chairs or bricks to hold the grid off the ground before pouring so the concrete fully encases the steel.