Enter a valid length.
Enter a valid width.
2026: #3=$0.55/ft #4=$0.80/ft #5=$1.20/ft
Total Linear Feet (with waste)
—
Was this calculator helpful?
Sources & Methodology
Rebar grid formula verified against Inch Calculator rebar material reference. ASTM A615 standard weights. ACI 318 spacing requirements for concrete reinforcement.
Inch Calculator — Rebar Material Calculator
Grid formula: bars = ceil(opposite dimension in inches / spacing) + 1. Edge clearance 3 inches. Common sizes: #3 driveways/patios, #4 residential slabs, #5 foundations.
Wellco Wholesale — How to Calculate Rebar in Concrete
ASTM A615 weight chart: #3=0.376, #4=0.668, #5=1.043, #6=1.502, #7=2.044, #8=2.670 lb/ft. Lap splice = 40× bar diameter. 10% waste standard for simple slabs.
ConcreteCalculate.com — Rebar Cost Calculator 2026
#4 rebar $0.65–$0.95/linear ft in 2026. Installation $0.75–$2.50/sq ft. Epoxy coating adds 30–50%. Labor $40–$75/hr for skilled ironworkers.
Formula: Bars along length = ceil(width_ft × 12 ÷ spacing_in) + 1, length = slab_length_ft. Bars along width = ceil(length_ft × 12 ÷ spacing_in) + 1, length = slab_width_ft. Total linear ft (before waste) = (bars_L × slab_length) + (bars_W × slab_width). With waste = total × (1 + waste%). Weight = total_ft × ASTM_weight_per_ft. Cost = total_ft × price_per_ft.
⏱ Last reviewed: April 2026
How to Calculate Reinforcement Rebar for a Concrete Slab
Calculating the amount of reinforcing bar (rebar) needed for a concrete slab is a straightforward grid calculation, but getting it right is critical — too little rebar and the slab is structurally weak; too much and you waste money and make concrete placement more difficult. The calculation depends on three variables: the area dimensions, the bar spacing, and the bar size specified for your project.
Rebar is placed in a grid pattern with bars running in two perpendicular directions. To find the number of bars in each direction, you divide the perpendicular dimension by the spacing interval and add one for the last bar at the edge. The total linear footage is the sum of all bars in both directions, multiplied by a waste factor to account for lap splices, cuts, and damaged pieces.
Rebar Quantity Formula
Bars (length direction) = ceil(Width_in ÷ Spacing_in) + 1 @ Length_ft each
Bars (width direction) = ceil(Length_in ÷ Spacing_in) + 1 @ Width_ft each
Total Linear Ft = (Bars_L × Length) + (Bars_W × Width)
With Waste = Total × (1 + Waste%)
Example — 20 ft × 30 ft slab, #4 rebar, 18″ spacing, 10% waste:
Bars along length = ceil(240″ ÷ 18) + 1 = ceil(13.3) + 1 = 15 bars @ 30 ft
Bars along width = ceil(360″ ÷ 18) + 1 = ceil(20) + 1 = 21 bars @ 20 ft
Total = (15 × 30) + (21 × 20) = 450 + 420 = 870 linear ft
With 10% waste = 870 × 1.10 = 957 linear feet to order
Weight = 957 × 0.668 = 639 lbs | Cost at $0.80/ft = $766
Bars along length = ceil(240″ ÷ 18) + 1 = ceil(13.3) + 1 = 15 bars @ 30 ft
Bars along width = ceil(360″ ÷ 18) + 1 = ceil(20) + 1 = 21 bars @ 20 ft
Total = (15 × 30) + (21 × 20) = 450 + 420 = 870 linear ft
With 10% waste = 870 × 1.10 = 957 linear feet to order
Weight = 957 × 0.668 = 639 lbs | Cost at $0.80/ft = $766
Rebar Size & Spacing Reference — By Application
| Application | Bar Size | Typical Spacing | Cost/Sq Ft (material) |
|---|---|---|---|
| Sidewalks & patios | #3 | 18″–24″ OC | $0.30–$0.50 |
| Driveways | #4 | 18″ OC | $0.45–$0.70 |
| Garage floors | #4 | 18″ OC | $0.50–$0.75 |
| Residential foundations | #4–#5 | 12″–18″ OC | $0.75–$1.20 |
| Retaining walls | #5 | 12″–16″ OC | $1.00–$1.50 |
| Commercial slabs | #5–#6 | 12″ OC | $1.25–$2.00 |
ASTM A615 Standard Rebar Weights
| Bar Size | Diameter | Weight (lb/ft) | Weight (kg/m) | 2026 Price/Linear Ft |
|---|---|---|---|---|
| #3 | 3/8″ (9.5mm) | 0.376 | 0.560 | $0.45–$0.65 |
| #4 | 1/2″ (12.7mm) | 0.668 | 0.994 | $0.65–$0.95 |
| #5 | 5/8″ (15.9mm) | 1.043 | 1.552 | $1.00–$1.40 |
| #6 | 3/4″ (19.1mm) | 1.502 | 2.235 | $1.40–$1.90 |
| #7 | 7/8″ (22.2mm) | 2.044 | 3.042 | $1.90–$2.50 |
| #8 | 1″ (25.4mm) | 2.670 | 3.973 | $2.40–$3.20 |
💡 Pro tip: Order rebar in standard 20-foot lengths for the lowest per-foot cost. Supplier cut charges of $1.50–$3.00 per cut add up quickly if you order custom lengths. For lap splices (where two bars overlap), minimum length is 40 times the bar diameter — that’s 20 inches for #4 rebar. Short lap splices are the most common rebar inspection failure. Always use rebar chairs (supports every 3–4 feet) to maintain proper cover depth of 1.5–3 inches from the slab bottom.
Frequently Asked Questions
Bars in length direction = ceil(Width_inches ÷ spacing) + 1, each Length_ft long. Bars in width direction = ceil(Length_inches ÷ spacing) + 1, each Width_ft long. Total linear ft = (bars_L × length) + (bars_W × width). Add 10% for waste. Multiply by ASTM weight per foot for total weight. Use this calculator for instant results with any dimensions.
#3 (3/8″) for sidewalks, patios, light slabs. #4 (1/2″) for residential driveways, garage floors, and standard slabs — the most common residential size. #5 (5/8″) for foundations, retaining walls, and heavier loads. #6 (3/4″) for heavy commercial slabs and structural elements. Always follow engineer specifications and local building codes for structural applications.
18–24 inches on center for residential patios and driveways. 12–18 inches for garage floors. 12 inches maximum for foundations and footings per most building codes. 18 inches is the most common for general residential slabs. ACI 318 limits maximum spacing to 3 times the slab thickness (not exceeding 18 inches) for temperature and shrinkage control reinforcement.
#3 rebar: $0.45–$0.65/ft. #4 rebar (most common): $0.65–$0.95/ft. #5 rebar: $1.00–$1.40/ft. #6 rebar: $1.40–$1.90/ft. Epoxy coating adds 30–50%. Order in standard 20-foot sticks for best pricing. By ton: approximately $800–$950/ton depending on size and region. Full installation (material + labor) runs $0.75–$2.50/sq ft for residential slabs.
ACI 318 minimums: 1.5 inches for interior slabs not exposed to weather. 2 inches for exterior slabs exposed to weather. 3 inches for concrete cast against ground (footings). Always use rebar chairs every 3–4 feet to maintain cover. Insufficient cover leads to premature corrosion, rust staining, and structural failure. Inspectors check cover depth before approving concrete pours.
Use rebar for driveways, garage floors, foundations, and any slab supporting vehicles or significant loads. Wire mesh (welded wire fabric) is adequate for thin decorative slabs, sidewalks, and low-load applications where crack control is the main goal. For any structural application or anything subject to heavy loads, #4 rebar at 18-inch spacing is significantly stronger and more reliable than wire mesh.
ASTM weights: #3=0.376 lb/ft, #4=0.668 lb/ft, #5=1.043 lb/ft, #6=1.502 lb/ft, #7=2.044 lb/ft, #8=2.670 lb/ft. Multiply total linear feet by weight per foot. Convert to tons by dividing by 2,000. Example: 957 ft of #4 rebar = 957 × 0.668 = 639 lbs = 0.32 tons. At $850/ton material cost = $272 for the rebar steel alone.
10% for simple rectangular slabs with no openings. 15% for slabs with corners, multiple openings, or L-shapes. 20% for complex shapes, curved walls, or heavily reinforced structural elements. Waste accounts for lap splices (minimum 20 inches for #4), end cuts, and damaged bars. Always round up to the nearest full 20-foot stick when ordering.
Minimum lap splice = 40 times bar diameter. #3: 40 × 0.375″ = 15″ minimum. #4: 40 × 0.5″ = 20″ minimum. #5: 40 × 0.625″ = 25″ minimum. #6: 40 × 0.75″ = 30″ minimum. Short lap splices are the #1 rebar inspection failure. Factor lap splice length into your total linear footage estimate, especially for long walls or large slabs requiring multiple bar lengths.
Yes for rectangular areas. For a wall, enter the wall length as Length and wall height as Width, then choose one-way pattern if bars run in only one direction (horizontal or vertical). For footings, enter footing length and width. For multiple parallel bars (e.g., 3 longitudinal bars in a footing), multiply the result by the number of bar rows and adjust accordingly. For complex structural elements, always follow the engineer’s drawings.
Related Calculators
Popular Calculators
Board Footage Calculator
Construction
Brick Calculator
Construction
AC Tonnage Calculator
Construction
Boiler Size Calculator
Construction
Stripe Fee Calculator
Finance
Pain & Suffering
Legal
TDEE Calculator
Health
Roofing Calculator
Construction
GPA Calculator
Education
Mortgage Refinance
Finance
CPM Calculator
Marketing
Markup Calculator
Finance