🔩 Rebar Calculator
Calculate rebar needed for concrete slabs and foundations
Common: 12", 16", or 18" spacing
How to Use This Calculator
Enter Slab Dimensions
Input the length and width of your concrete slab or foundation in feet. Measure the area where you'll be placing rebar reinforcement.
Set Rebar Spacing
Enter the spacing between rebar in inches. Common spacing is 12 inches (1 foot), 16 inches, or 18 inches. Closer spacing provides more reinforcement.
Select Rebar Size
Choose the rebar size from the dropdown. #4 rebar (1/2 inch) is most common for slabs. Larger sizes (#5, #6) are used for heavier loads and foundations.
Calculate and Order
Click "Calculate Rebar" to see total weight, length, and number of pieces needed. Add 5-10% extra for cuts, overlaps, and waste.
Formula
Rebars in Length = (Length ÷ Spacing) + 1
Rebars in Width = (Width ÷ Spacing) + 1
Total Length = (Rebars in Length × Width) + (Rebars in Width × Length)
Total Weight = Total Length × Weight per Foot
Example 1: Slab (20 ft × 12 ft, #4 rebar, 12" spacing)
Step 1: Rebars lengthwise = (20 ÷ 1) + 1 = 21 pieces
Step 2: Rebars widthwise = (12 ÷ 1) + 1 = 13 pieces
Step 3: Lengthwise feet = 21 × 12 = 252 ft
Step 4: Widthwise feet = 13 × 20 = 260 ft
Step 5: Total length = 252 + 260 = 512 linear feet
Step 6: Weight = 512 × 0.668 = 342 lbs (0.17 tons)
Example 2: Foundation (30 ft × 15 ft, #5 rebar, 16" spacing)
Step 1: Spacing = 16" = 1.33 ft
Step 2: Rebars lengthwise = (30 ÷ 1.33) + 1 = 24 pieces
Step 3: Rebars widthwise = (15 ÷ 1.33) + 1 = 13 pieces
Step 4: Total length = (24 × 15) + (13 × 30) = 360 + 390 = 750 linear feet
Step 5: Weight = 750 × 1.043 = 782 lbs (0.39 tons)
About Rebar Calculator
The Rebar Calculator is an essential tool for contractors, concrete contractors, engineers, and builders who need to accurately determine how much rebar (reinforcing steel) is required for concrete slabs, foundations, and structural elements. This calculator eliminates guesswork by providing precise rebar quantities, weights, and layout information based on slab dimensions and spacing requirements.
When to Use This Calculator
- Concrete Slabs: Calculate rebar needed for driveways, patios, garage floors, and flatwork
- Foundations: Determine rebar quantities for footings, foundation walls, and structural slabs
- Structural Work: Estimate rebar for beams, columns, and other reinforced concrete elements
- Commercial Projects: Plan materials for larger commercial concrete projects and renovations
- Budget Planning: Estimate costs by calculating rebar weight and quantity needed
Why Use Our Calculator?
- ✅ Accurate Quantities: Calculates exact number of rebar pieces and total linear feet needed
- ✅ Weight Calculation: Provides total weight in pounds, tons, and kilograms for ordering
- ✅ Multiple Sizes: Supports all standard rebar sizes from #3 to #18
- ✅ Layout Information: Shows grid layout with spacing and piece counts for each direction
- ✅ Cost Estimation: Helps budget accurately by determining exact material needs
- ✅ Time Savings: Instant calculations eliminate manual counting and math errors
Common Applications
Residential Construction: Homeowners and contractors planning concrete slabs, driveways, or foundations use this calculator to order the correct quantity of rebar. It prevents costly mistakes from ordering too little or too much rebar and helps coordinate with suppliers for delivery scheduling.
Commercial Projects: Contractors and engineers working on larger projects rely on accurate rebar calculations for project estimates, material orders, and cost calculations. This tool provides quick reference for bidding and ensures sufficient materials are on-site before starting work.
Engineering Design: Structural engineers use rebar calculations to verify reinforcement requirements and ensure concrete structures meet design specifications and building codes.
Tips for Best Results
- Standard Spacing: Use 12" spacing for slabs, 16-18" for foundations; closer spacing for heavy loads
- Rebar Sizes: #4 (1/2") is common for slabs; #5-#6 for foundations and heavy loads
- Add Waste: Always add 5-10% extra rebar for cuts, overlaps at joints, and waste
- Overlap Requirements: Account for overlaps where rebar pieces meet (typically 40× bar diameter)
- Order in Lengths: Standard rebar comes in 20-foot lengths; adjust calculations for custom lengths
Frequently Asked Questions
How much rebar do I need for a 20×12 foot concrete slab?
For a 20×12 foot slab with #4 rebar at 12" spacing, you'll need approximately 512 linear feet of rebar, weighing about 342 pounds (0.17 tons). This includes both lengthwise and widthwise reinforcement in a grid pattern.
What size rebar should I use for a concrete slab?
#4 rebar (1/2 inch diameter) is standard for most residential slabs. For heavier loads, driveways with vehicle traffic, or foundations, use #5 (5/8 inch) or #6 (3/4 inch) rebar. Consult building codes for specific requirements.
What spacing should I use for rebar?
Standard spacing is 12 inches (1 foot) for slabs and patios. Foundations and heavy-duty slabs often use 16-18 inch spacing. Closer spacing (10-12 inches) provides more reinforcement but costs more. Check local building codes for requirements.
Do I need to add extra rebar for overlaps?
Yes! Add 5-10% extra rebar for overlaps where pieces connect (typically 40× bar diameter overlap), cuts, and waste. For #4 rebar, overlaps are about 20 inches; for #5, about 25 inches.
How much does rebar cost?
Rebar prices vary by region and market conditions, typically $0.50-$1.50 per pound for #4-#6 rebar. Prices fluctuate with steel market conditions. Order early and compare suppliers for best pricing.
Can I use this for two-way reinforcement (mesh pattern)?
Yes! This calculator assumes standard two-way reinforcement with rebar running in both directions. It calculates the grid pattern automatically based on your spacing input. Make sure rebar is tied at intersections.