Calculate rebar quantity, weight, and cost for any concrete project. Accounts for bar size, spacing, lap splices, waste, and support chairs.
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49 standard 20-ft bars, 650 lbs
| Slab Area | 576 sq ft |
|---|---|
| Bars (lengthwise) | 17 |
| Bars (widthwise) | 17 |
| Total Bar Count | 34 |
| Base Linear Feet | 816 |
| Splice Linear Feet | 68 |
| Total Linear Feet (w/ waste) | 972 |
| Standard 20-ft Bars | 49 |
| Total Weight | 650 lbs |
| Rebar Cost | $777.92 |
| Chairs Needed | 234 |
| Chair Cost | $51.48 |
| Grand Total | $829.40 |
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Rebar is designated by number, which represents the diameter in eighths of an inch. Number 3 rebar is 3/8 inch (9.5mm) diameter, number 4 is 1/2 inch (12.7mm), number 5 is 5/8 inch (15.9mm), and number 6 is 3/4 inch (19.1mm). The cross-sectional area increases with the square of the diameter, so number 5 rebar has 56 percent more steel area than number 4, not just 25 percent more.
For residential construction, number 4 rebar handles the vast majority of applications. It provides excellent crack control for slabs, adequate reinforcement for low retaining walls, and sufficient flexural strength for residential footings. Number 3 is used for temperature and shrinkage steel in slabs where structural reinforcement is not needed. Number 5 is specified for taller retaining walls, deeper footings, and structural elements that carry significant loads. Using a larger bar size than needed wastes money, but using a smaller size compromises structural integrity.
Rebar spacing is always specified as center-to-center distance between adjacent parallel bars. Common specifications include 12 inches on center, 16 inches on center, 18 inches on center, and 24 inches on center. Tighter spacing provides more reinforcement per square foot. For a given area, 12-inch spacing uses 50 percent more rebar than 18-inch spacing.
Standard residential specifications call for number 4 at 18 inches on center each way for 4-inch slabs, number 4 at 12 inches for driveways and garage floors, and number 5 at 12 inches for structural slabs and retaining walls. These specifications may be increased by the structural engineer based on soil conditions, loading requirements, and seismic zone. Always follow the engineering drawings rather than rule-of-thumb guidelines for any permitted construction.
Accurate rebar estimation requires counting bars in each direction and accounting for lap splices. For a rectangular slab, divide the width by the spacing and add one to get the number of bars running lengthwise. Repeat for the perpendicular direction. Multiply bar count by bar length to get linear footage in each direction.
Lap splices are needed wherever bars must be joined, which happens when the slab dimension exceeds the standard 20-foot bar length. The minimum lap splice length is 40 bar diameters: 15 inches for number 3, 20 inches for number 4, 25 inches for number 5, and 30 inches for number 6. Many specifications round up to 24 inches minimum for simplicity. Count the number of splices and multiply by splice length to get additional linear footage. Add this to the base linear footage, then apply a 10 percent waste factor for the final order quantity.
In 2026, rebar pricing varies by size and market. Number 3 costs $0.50 to $0.65 per linear foot or approximately $10 to $13 per 20-foot bar. Number 4 costs $0.70 to $0.90 per foot or $14 to $18 per bar. Number 5 costs $1.00 to $1.30 per foot or $20 to $26 per bar. Number 6 costs $1.40 to $1.80 per foot or $28 to $36 per bar. For a typical 24x24-foot slab with number 4 at 18-inch spacing, the rebar cost is approximately $600 to $750 including waste and splices. Adding rebar chairs at $0.15 to $0.30 each brings the total reinforcement cost to $650 to $850. This represents roughly $1.15 to $1.50 per square foot of slab area for reinforcement alone.
Welded wire reinforcement (WWR), commonly called wire mesh, consists of steel wires welded together in a grid pattern. The most common residential specification is 6x6 W1.4/W1.4, meaning wires spaced 6 inches apart in both directions with a wire diameter of approximately 0.135 inches. Wire mesh comes in flat sheets (typically 5x10 feet) or rolls (5 feet wide by 150 feet long).
Wire mesh costs approximately $85 per 150-square-foot roll or $0.57 per square foot. Installation is straightforward but achieving proper placement is challenging. Mesh must sit at the mid-depth of the slab, not on the ground or resting on the subgrade. Common practice of placing mesh flat on the ground and attempting to pull it up during concrete placement ("hooking") is unreliable. The mesh often ends up at the bottom of the slab where it provides minimal benefit. Proper installation requires mesh supports (similar to rebar chairs) placed at regular intervals.
Rebar provides significantly better crack control and structural reinforcement than wire mesh. Number 4 rebar at 18-inch spacing provides approximately 3 times the steel area per square foot compared to 6x6 W1.4 mesh. Rebar is also much easier to properly position within the slab using rebar chairs, which are designed specifically for this purpose and maintain consistent bar height throughout the pour.
The primary advantage of rebar is its reliability. When properly placed on chairs, rebar stays at the correct depth throughout the concrete placement process. This consistency means the reinforcement performs as designed. With wire mesh, placement inconsistencies are common and can result in sections of the slab with reinforcement at the wrong depth or bunched up in the middle of a panel.
Synthetic and steel fiber reinforcement is a third option that has gained popularity for residential slabs. Synthetic fibers (polypropylene or nylon) are mixed directly into the concrete at the batch plant at a rate of 1 to 3 pounds per cubic yard, adding $6 to $12 per cubic yard to the concrete cost. They help control plastic shrinkage cracking but do not replace structural reinforcement. Steel fibers at 40 to 60 pounds per cubic yard provide structural reinforcement equivalent to light wire mesh and cost $30 to $50 per cubic yard extra.
The main advantage of fiber reinforcement is the elimination of placement labor. There are no chairs to set, no mesh to cut and position, and no bars to tie. For lightly loaded residential slabs like patios and walkways, synthetic fiber reinforcement combined with proper joint spacing is a cost-effective solution. However, for driveways, garage floors, and any structural application, fiber reinforcement should supplement rather than replace rebar or mesh.
For a 20x20-foot (400 sq ft) slab at 4 inches thick, the reinforcement costs compare as follows. Wire mesh: $230 to $280 (materials) plus $100 to $150 (labor) equals $330 to $430 total. Rebar number 4 at 18 inches: $350 to $450 (materials including chairs) plus $200 to $300 (labor) equals $550 to $750 total. Synthetic fiber: $18 to $36 added to concrete cost, with no placement labor. Steel fiber: $90 to $150 added to concrete cost. For non-structural slabs, synthetic fiber offers the best value. For any load-bearing application, rebar provides the most reliable and cost-effective long-term solution despite higher upfront cost.
Number 3 (3/8 inch) rebar is used for patios and walkways. Number 4 (1/2 inch) is standard for residential slabs, driveways, and walls. Number 5 (5/8 inch) is for foundations, retaining walls, and structural elements. Number 6 and larger are for commercial and heavy structural applications.
For residential slabs, 18 inches on center is standard. Driveways and garage floors use 12 to 16 inches on center. Structural slabs typically require 12 inches on center or less. The spacing is measured center-to-center of adjacent bars in both directions.
In 2026, number 3 rebar costs $0.50 to $0.65 per foot, number 4 costs $0.70 to $0.90 per foot, number 5 costs $1.00 to $1.30 per foot, and number 6 costs $1.40 to $1.80 per foot. Prices vary by region, quantity, and whether bars are cut to length or sold in standard 20-foot lengths.
The minimum lap splice length is 40 bar diameters. For number 4 rebar, this is 20 inches. For number 5, it is 25 inches. For number 3, it is 15 inches. Many engineers specify 24 inches minimum for simplicity. Splices should be staggered, not all in the same location.
Rebar is commonly sold in 20-foot lengths. Some suppliers offer 40-foot and 60-foot lengths for commercial projects. Cut-to-length service is available at most rebar suppliers for an additional fee of $0.05 to $0.15 per cut.
Number 3 rebar weighs 0.376 lbs/ft, number 4 weighs 0.668 lbs/ft, number 5 weighs 1.043 lbs/ft, number 6 weighs 1.502 lbs/ft, and number 7 weighs 2.044 lbs/ft. Multiply by total linear footage to get total weight.
Yes. Rebar must be supported at the correct height within the slab, typically at the middle third of the slab thickness. Rebar chairs (supports) are placed every 3 to 4 feet along each bar. For a 4-inch slab, use 1.5-inch chairs. Standard chairs cost $0.15 to $0.30 each.
Wire mesh (6x6 W1.4/W1.4) works for lightly loaded 4-inch slabs like patios and sidewalks. Rebar is superior for driveways, garage floors, structural slabs, and any thickness over 4 inches. Wire mesh costs less but does not provide the same crack control as properly placed rebar.
Bars per direction = (width / spacing) + 1
Linear ft = bars x length per bar + splice overlap
Weight = linear ft x weight per ft (varies by bar size)
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