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Rebar Calculator

Calculate exactly how much rebar you need for your concrete slab, footing, or wall. Enter your slab dimensions, choose the rebar size and grid spacing, and this calculator gives you the number of pieces in each direction, total linear feet, total weight in pounds and tons, and an estimated cost. Covers standard rebar sizes #3 through #8.

Longer dimension
Shorter dimension
Typically 3" from slab edge
US average: $800–1,200/ton. Varies by size and region.

📊 Rebar Estimate

Slab Area—
Rebar Size—
Grid Spacing—
Pieces — Lengthwise (long)—
Pieces — Crosswise (short)—
Each Piece Length (approx)—
Total Linear Feet—
Total Weight (lbs)—
Total Weight (tons)—
Estimated Cost—
Includes overlap/splice length (40× bar diameter). Excludes stirrups and chairs — add ~5–10% for accessories.

How to Use the Rebar Calculator

Enter your slab length and width in feet. The calculator assumes rebar runs in both directions (a grid pattern) — lengthwise and crosswise bars. Select your rebar size based on your project needs: #3 (3/8") for residential patios and sidewalks, #4 (1/2") for standard driveways and garage slabs, #5 (5/8") for heavy-duty slabs and commercial floors.

Grid spacing is the distance between parallel bars. Twelve inches on center is standard for residential slabs. Six-inch spacing provides heavier reinforcement for driveways or slabs that will bear vehicle loads. Eighteen to 24-inch spacing is acceptable for sidewalks and light-use patios.

Overlap (lap splice): When a slab dimension exceeds the standard rebar length (typically 20 feet), bars must be overlapped and tied together. The standard Class B tension lap splice is 40 times the bar diameter — for #4 rebar (0.5" diameter), that's a 20-inch overlap. The calculator uses this overlap length to determine the total piece length, which may exceed the slab dimension slightly.

Weight calculation: Each rebar size has a standard weight per linear foot, defined by ASTM A615:

Bar Size Diameter (in) Weight (lb/ft) Common Use
#30.3750.376Patios, sidewalks, residential slabs
#40.5000.668Driveways, garage floors, standard slabs
#50.6251.043Footings, heavy slabs, retaining walls
#60.7501.502Foundation walls, columns
#70.8752.044Commercial beams, bridge decks
#81.0002.670Heavy structural, columns

Rebar Installation Tips

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Frequently Asked Questions

For residential slabs on grade (patios, sidewalks): #3 (3/8") rebar at 18–24 inch spacing is sufficient. For driveways and garage floors: #4 (1/2") at 12–16 inch spacing is standard. For commercial floors or slabs that will bear heavy loads: #5 (5/8") at 12 inch spacing. Always check local building codes — some municipalities require #4 minimum for any occupied structure slab. Wire mesh (WWF) is an alternative for thin non-structural slabs but provides less crack control than rebar.
Rebar prices fluctuate with the steel market. As of 2026, expect $800–1,200 per ton for common sizes (#3–#6) from a steel supplier. #3 rebar runs about $4–6 per 20-foot stick, #4 about $7–10 per stick, and #5 about $12–17 per stick. Home improvement stores charge a premium — often 30–50% more than a dedicated steel yard. For a standard 20×12 garage slab with #4 rebar at 12" spacing, expect to pay about $300–450 for rebar material.
Rebar (reinforcing bar) is individual steel bars placed in a grid pattern, providing high tensile strength and crack control. Wire mesh (welded wire fabric, or WWF) is a pre-welded grid of thinner wire, typically 6×6 W2.9/W2.9. Rebar is stronger and better for structural slabs, driveways, and any slab over 4 inches thick. Wire mesh is cheaper, easier to install, and adequate for residential patios, sidewalks, and 4-inch slabs. Many contractors prefer rebar because mesh tends to get pushed to the bottom during the pour if not properly chaired.
Standard concrete cover for slabs on grade is 3 inches from all edges. This means the outermost rebar should be set 3 inches in from the slab perimeter. For slabs exposed to de-icing salts or in coastal areas, increase to 4 inches. For foundation walls and footings cast against earth, code requires 3 inches of cover. The calculator automatically subtracts edge clearance from your slab dimensions when computing bar lengths.
Rebar weight is based on its diameter squared: Weight (lb/ft) = diameter² (in inches) × 2.67. For example, #4 rebar is 1/2" diameter: 0.5² × 2.67 = 0.668 lb/ft. The total weight is simply total linear feet × weight per foot. A 20-foot stick of #4 rebar weighs about 13.4 pounds. There are exactly 2,000 pounds in a ton. Our calculator uses ASTM A615 standard weights for each bar size and converts automatically.