Professional Rebar Calculator - Calculate Rebar Weight, Quantity & Cost for Concrete
Calculate rebar weight, quantity, and cost for concrete slabs, foundations, walls, and footings. Get accurate estimates for rebar spacing, overlap length, and total material requirements with support for imperial and metric rebar sizes.
Project Dimensions
Select your concrete project type
Longest dimension of slab
Shorter dimension of slab
Common: 6-18 inches
Typical grid spacing: 12-18 inches
Slabs over 6" typically use 2 layers
Total Rebar:
37 bars
635.00 ft total length
Rebar Specifications
Selected Rebar Size
#4 (1/2") - Standard residential slabs and driveways
Standard stock lengths from suppliers
Minimum: 20" (40× diameter)
Interior: 3/4", Exterior: 1.5-2"
Prices vary by size and grade
Additional Costs
Total Weight:
424.18 lbs
36 stock bars needed
Cost & Material Analysis
Project Summary
Material Calculations
Cost Breakdown
Unit Costs
Professional Recommendations
- • Consider epoxy-coated rebar for outdoor slabs to prevent corrosion and extend service life
Rebar Information
Standard Grade 60 steel with 60,000 psi yield strength, suitable for most applications
Last updated: November 5 2025
Curated by the QuickTooly Team
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What Is a Rebar Calculator? Complete Guide to Concrete Reinforcement
A rebar calculator is a professional tool for accurately estimating the quantity, weight, and cost of reinforcing steel (rebar) needed for concrete construction projects. This comprehensive calculator determines rebar requirements for slabs, foundations, walls, footings, columns, and beams by calculating grid spacing, overlap lengths, and material quantities. Support for both imperial (#3-#11) and metric (6mm-32mm) rebar sizes ensures accurate estimates for any construction project worldwide.
Our advanced rebar calculator handles various project types including slabs, walls, and footings, accounts for multiple rebar grades and coatings, calculates proper spacing and concrete cover, determines the number of stock bars needed accounting for overlap, and provides complete cost analysis including labor and accessories. Perfect for contractors, engineers, estimators, and DIY builders planning concrete projects.
Why Use Our Professional Rebar Calculator?
- Accurate Quantity Estimates: Precise calculations for rebar quantity based on project dimensions, spacing requirements, and number of layers. Accounts for overlap and wastage to ensure adequate material ordering.
- Multiple Project Types: Support for slabs, walls, footings, columns, and beams with appropriate rebar configurations and spacing recommendations for each application type.
- Weight Calculations: Automatic weight calculations using accurate rebar densities for all standard sizes. Critical for delivery planning, crane capacity, and labor estimation.
- Complete Cost Analysis: Detailed cost breakdowns including rebar material, tying wire and labor, rebar chairs and supports, and delivery charges with multi-currency support.
- Professional Recommendations: Expert guidance on spacing requirements, overlap lengths, concrete cover, rebar grades, and cost-saving strategies based on project specifications.
Rebar Sizes Guide: Imperial & Metric Standards
Imperial Rebar Sizes (United States)
#3 (3/8" diameter, 0.376 lb/ft): Smallest common size for light residential slabs and driveways. Minimum size for most code requirements.
#4 (1/2" diameter, 0.668 lb/ft): Most common residential rebar for 4-6" slabs, sidewalks, and light footings. Good balance of cost and strength.
#5 (5/8" diameter, 1.043 lb/ft): Standard for thicker slabs (6"+), heavy-duty driveways, and commercial applications. Excellent for high-traffic areas.
#6 (3/4" diameter, 1.502 lb/ft): Common in commercial construction, retaining walls, and structural foundations. Required for heavily loaded slabs.
#7-#8 (7/8"-1" diameter): Heavy construction, bridge decks, and structural beams. Used where significant loads or long spans require maximum strength.
#9-#11 (1.128"-1.41" diameter): Large-scale commercial and industrial projects, columns, and heavy structural members. Special order items requiring planning.
Metric Rebar Sizes (International)
6-8mm: Light residential applications, mesh reinforcement, and non-structural elements. Common in European and Asian construction.
10-12mm: Standard residential slabs and walls. Equivalent to imperial #3-#4. Most common sizes for home construction worldwide.
16-20mm: Commercial construction, thicker slabs, and structural applications. Equivalent to imperial #5-#6. Heavy-duty residential and light commercial standard.
25-32mm: Heavy structural work, columns, beams, and industrial foundations. Used in multi-story buildings and infrastructure projects.
Rebar Spacing Requirements & Standards
- Residential Slabs (Light Duty): Standard spacing 12-18 inches (30-45 cm) on center both directions. #3 or #4 rebar adequate for most 4" slabs. Single layer at mid-depth sufficient for garage floors and patios.
- Commercial Slabs (Heavy Duty): Tighter spacing 8-12 inches (20-30 cm) required for higher loads. #5 or #6 rebar standard for 6"+ slabs. Double layer recommended for warehouse and industrial floors supporting heavy equipment.
- Footings & Foundations: Minimum 2 bars top and bottom for continuous footings. Spacing 12-24 inches perpendicular. Larger footings require #5 or #6. Dowels into walls every 24-48 inches for proper connection.
- Walls (Vertical): Vertical bars every 12-24 inches depending on wall height and loading. Horizontal bars at top, bottom, and mid-height minimum. #4 or #5 standard for 6-8" walls. Increase size and reduce spacing for retaining walls.
- Columns: Minimum 4 vertical bars with ties every 12-16 inches. Bar size depends on column load and height. #5-#8 typical for residential to light commercial. Follow structural engineer specifications.
- Beams & Lintels: Bottom reinforcement in tension zone critical. Top bars over supports. Stirrups (ties) required for shear resistance. Size and spacing per structural design - don't estimate beam reinforcement.
Understanding Rebar Grades & Special Coatings
- Grade 60 (Standard - 60,000 psi): Most common grade for residential and commercial construction. Excellent balance of strength, ductility, and cost. Suitable for 95% of applications. Industry standard in North America.
- Grade 40 (Light Duty - 40,000 psi): Lower strength steel for light-duty applications. Less common, mainly used where design specifically calls for more ductility. Lower cost but not recommended as substitute for Grade 60.
- Grade 75 (High Strength - 75,000 psi): Higher strength for specialized applications requiring less steel or tighter spacing. Premium cost. Used in seismic zones and high-load applications where design optimization justified.
- Epoxy Coated Rebar: Green epoxy coating protects against corrosion in harsh environments. Essential for bridge decks, parking structures, and marine applications. Costs 20-40% more but extends service life significantly. Handle carefully to avoid coating damage.
- Galvanized Rebar: Zinc coating provides excellent corrosion resistance for outdoor and marine use. More expensive than epoxy but superior in extremely aggressive environments. Commonly specified near coastlines and for water treatment facilities.
- Stainless Steel Rebar: Premium option with maximum corrosion resistance. Costs 8-10× standard rebar but virtually maintenance-free. Reserved for critical infrastructure, historic restoration, and structures requiring 100+ year service life.
Concrete Cover Requirements for Rebar Protection
Concrete cover is the distance from rebar surface to concrete surface. Adequate cover protects rebar from corrosion, provides fire resistance, and ensures proper bond with concrete. Building codes specify minimum cover based on exposure conditions.
Interior Slabs (Dry Conditions)
Minimum 3/4" (19mm) cover for slabs and walls. Standard 1.5" (38mm) provides better protection. Use plastic chairs or bar supports to maintain position during concrete placement.
Exterior Slabs & Exposed Concrete
Minimum 1.5" (38mm) for slabs and 2" (50mm) for walls exposed to weather. Increase to 2" (50mm) for freeze-thaw climates and 3" (75mm) near coastlines for corrosion protection.
Footings & Below-Grade Concrete
Minimum 3" (75mm) when cast against earth. Increase to 4-6" for footings in aggressive soils. Use vapor barrier when possible to reduce soil contact and moisture exposure.
Columns & Beams
1.5" (38mm) minimum for interior, 2" (50mm) for exterior. Large columns (over 12") require 2" minimum. Ties and stirrups require 1.5" cover to outside of main bars.
Rebar Lap Splice & Overlap Length Requirements
Rebar overlap (lap splice) is where two bars overlap to create continuous reinforcement. Adequate lap length ensures load transfer between bars without bond failure. Lap length depends on bar size, concrete strength, and bar grade.
Standard Lap Length Formula
Minimum lap = 40 × bar diameter for Grade 60 in 3000 psi concrete. For #4 bar (0.5" diameter): 40 × 0.5" = 20" minimum. For #5 bar: 40 × 0.625" = 25" minimum. Always round up to nearest 6" increment.
Common Lap Lengths by Bar Size
#3: 15-18 inches | #4: 20-24 inches | #5: 24-30 inches | #6: 30-36 inches | #7: 36-42 inches | #8: 42-48 inches. Use longer laps for lower concrete strength or aggressive exposure.
Lap Splice Best Practices
Stagger laps to avoid weak plane - don't lap all bars in same location. Lap at low-stress areas, typically near mid-span for slabs. Tie laps with wire at each end and middle. For walls, alternate laps on adjacent bars by at least 24".
When Increased Lap Length Required
Double the standard lap for: bars spliced in tension zones at maximum stress, epoxy coated rebar (reduced bond), lightweight concrete, or when specified by structural engineer. Never reduce lap below code minimum.
Rebar Installation Best Practices & Common Mistakes
- Proper Support & Positioning: Use manufactured rebar chairs, not wood blocks or stones. Position rebar at proper depth - mid-depth for single layer slabs. Tie intersections with wire to prevent movement during concrete pour. Check position before and during concrete placement.
- Maintaining Concrete Cover: Biggest installation mistake is inadequate concrete cover. Rebar too close to surface leads to corrosion and spalling. Use proper height chairs and side spacers. Don't step on rebar during pour - repositions bars downward.
- Clean Bar Surface: Remove loose rust, mud, and oil before concrete placement. Light surface rust acceptable and actually improves bond. Heavy flaking rust reduces bar diameter and bond - reject and replace. Store rebar off ground on blocks.
- Proper Tying Technique: Tie all intersections in grid pattern. Use 16-18 gauge tie wire. Twist tie away from concrete surface to avoid rust staining. Pre-tied chairs speed installation but cost more. Don't over-tie - wire breaks and wastes time.
- Edge Distance Requirements: Maintain minimum 3" from slab edges to prevent corner cracks. Pull bars back from doorways and openings. Add diagonal bars at corners for crack control. Edge bars reduce perimeter curling in large slabs.
- Inspection Before Pour: Verify bar size, spacing, and lap lengths against plans. Check concrete cover with spacer blocks. Ensure chairs adequate for anticipated traffic during pour. Inspect all splices and tie wire. Take photos for documentation.
Critical Rebar Calculation & Installation Errors
- Insufficient Rebar Quantity: Forgetting to account for overlap wastes money and delays project. Standard 20-foot bars won't cover 20 feet of slab due to required 24" overlaps. Add 10-15% for waste, cutting, and overlaps. Better to over-order slightly than run short mid-pour.
- Wrong Bar Size Selection: Using #3 bar in 6" slab or #6 in 4" slab. Thicker slabs need larger bars and potentially two layers. Consult code requirements or engineer for proper sizing. Bar size affects spacing requirements and structural capacity.
- Inadequate Spacing: Spacing bars 24" on center when code requires 18" maximum. Wide spacing saves material but compromises structural integrity and crack control. Never exceed maximum spacing without engineering approval. Closer spacing sometimes required for shrinkage control.
- Ignoring Concrete Cover: Placing rebar directly on ground or formwork. Minimum cover requirements exist for corrosion protection and fire resistance. Use proper height chairs - different sizes for different slab depths. Inadequate cover causes premature concrete failure.
- Poor Lap Splice Execution: Using 12" overlap when 30" required for bar size. Lapping all bars at same location creates weak plane. Forgetting to tie laps allows separation. Insufficient lap length is structural deficiency requiring expensive repair or replacement.
- Rebar Position During Pour: Stepping on rebar grid collapses chairs and pushes bars down. Walking on wire mesh flattens it to ground. Position bars at correct depth and protect during concrete placement. Use planks over rebar to distribute worker weight.
Frequently Asked Questions About Rebar
What size rebar for 4 inch concrete slab?
#3 or #4 rebar at 18 inches on center both directions is standard for residential 4" slabs. #3 adequate for light duty (patios, sidewalks), #4 better for garage floors and driveways. Always check local codes - some jurisdictions require #4 minimum.
Do I need rebar in concrete slab?
Rebar significantly improves concrete performance by controlling cracks and adding structural capacity. Required by code for most structural slabs, footings, and walls. Small non-structural slabs (shed floors, walkways) may use wire mesh instead or omit reinforcement, but rebar is best practice.
How far apart should rebar be in concrete slab?
Standard residential spacing is 12-18 inches on center both directions. Commercial or heavy-duty applications require 8-12 inch spacing. Maximum spacing typically 18 inches unless engineer specifies wider. Closer spacing provides better crack control and load distribution.
How much does rebar cost per foot?
#4 rebar (most common) costs $0.50-0.85 per linear foot, depending on region and market. #3 runs $0.35-0.60/ft, #5 about $0.75-1.10/ft. Prices for stock 20-foot lengths: #4 ≈ $10-17, #5 ≈ $15-22. Add 20-40% for epoxy coated, more for galvanized or stainless.
Can I use wire mesh instead of rebar?
Wire mesh (welded wire fabric) suitable for thin slabs (3-4") with light loads. Provides crack control but less structural capacity than rebar. Mesh works for basement floors, sidewalks, and patios. Use rebar for driveways, structural slabs, and anywhere building code requires #3 or larger bars.
Where should rebar be positioned in slab?
Single layer at mid-depth (half thickness) for 4-6" slabs. Example: 4" slab has rebar at 2" depth (1.5-2" from bottom, 2-2.5" from top). Thicker slabs use two layers: bottom layer at 1/3 depth, top layer at 2/3 depth. Maintain minimum 1.5" cover from any surface.
How do you calculate number of rebar needed?
Divide slab length by bar spacing, add 1 for bars running lengthwise. Repeat for bars running crosswise (divide width by spacing, add 1). Multiply lengthwise bars × width and crosswise bars × length for linear footage. Divide by stock length (20 ft), round up, add 10% waste.
What is the difference between #3, #4, and #5 rebar?
Number indicates bar diameter in eighths of inch: #3 = 3/8", #4 = 4/8" (1/2"), #5 = 5/8". Weight increases dramatically with size: #3 = 0.376 lb/ft, #4 = 0.668 lb/ft, #5 = 1.043 lb/ft. Larger bars provide more strength and stiffness but cost and weigh more. Use smallest bar meeting structural requirements.
Start Your Concrete Project with Accurate Rebar Calculations
Use our professional rebar calculator to accurately estimate quantities, weights, and costs for your concrete slab, foundation, or structural project. Accurate rebar calculations ensure structural integrity, code compliance, and proper material ordering. Whether you're building a residential driveway, commercial foundation, or structural beam, knowing exact rebar requirements prevents costly shortages and installation delays. Consider project type, loading conditions, and environmental exposure when selecting rebar size and spacing. Proper installation with adequate concrete cover and lap lengths ensures long-lasting, crack-free concrete structures that meet or exceed building code requirements.