Quick answer: For a slab grid, divide each side by the bar spacing (usually 12–18 in) and add one per direction, then multiply. Common sizes: #4 (1/2 in) for slabs, #5 (5/8 in) for footings.
Enter your slab size and grid spacing to find how many rebar bars, total linear feet, and 20-foot sticks you need.
For a flat slab or footing, rebar is laid in a grid. The number of bars in each direction depends on the slab dimension perpendicular to the bars, the on-center spacing, and the edge clearance (concrete cover). The formulas are:
Bars = ((dimension − 2 × clearance) ÷ spacing) + 1
Bars running the length of the slab are spaced across its width, and bars running the width are spaced along its length. Multiply each bar count by its length to get linear feet, then divide by 20 (the standard stick length) and round up to get the number of sticks to buy.
#4 rebar (1/2 inch) weighs 0.668 lb per foot, so a standard 20 ft stick is about 13.4 lb. Rebar is priced by weight but sold by the stick, which is why estimates drift — convert your total linear feet to pounds before pricing.
| Bar size | Diameter | Weight per ft | Weight per 20 ft stick |
|---|---|---|---|
| #3 | 3/8 in | 0.376 lb | 7.5 lb |
| #4 | 1/2 in | 0.668 lb | 13.4 lb |
| #5 | 5/8 in | 1.043 lb | 20.9 lb |
| #6 | 3/4 in | 1.502 lb | 30 lb |
Lay out a grid at your chosen spacing (commonly 18 inches on center for residential slabs), count the bars in each direction, and total the linear feet. A 12 x 20 ft slab at 18-inch spacing needs roughly 300 linear feet, or about sixteen 20-foot sticks with waste.
Residential slabs commonly use #4 (1/2-inch) bar at 16 to 18 inches on center. Heavier structural slabs and footings may call for 12-inch spacing. Always follow the engineered drawing when one exists.
Standard rebar is sold in 20-foot lengths, though 10- and 40-foot lengths are also available. This calculator uses 20 feet to estimate stick count.
Budget about 10% extra to cover lap splices, miscuts, and damaged bar.
Last reviewed August 2026 · how we source these figures
Every constant this calculator uses and where it comes from, so you can check it rather than take our word for it.
Local codes amend the model IRC and adopt different cycles — your building department governs. Manufacturers revise yields; where your product's data sheet disagrees with a default here, use the product's number. See our full methodology.