Rebar Calculator
Calculate rebar quantity, weight, and spacing for concrete slabs, footings, and walls. Includes lap splice calculations and bar bending schedules.
Project Type
Dimensions
Rebar Size
#4 = 0.5" dia, 0.668 lb/ft
Spacing
Related Calculators
About This Calculator
The Rebar Calculator determines exactly how much reinforcing steel you need for concrete slabs, footings, walls, and foundations—with accurate quantities, weights, lap splice requirements, and 2026 cost estimates. Reinforcing bar (rebar) transforms concrete from a brittle material into a structural powerhouse capable of handling tension, compression, and seismic forces.
Getting rebar quantity and spacing right is critical for structural integrity. Under-reinforced concrete cracks and fails; over-reinforced concrete wastes money. Our calculator handles the complex math of grid spacing, lap splices, concrete cover, and material weight to provide professional-grade estimates for any concrete project.
Whether you're reinforcing a garage slab, pouring a foundation footing, building a retaining wall, or constructing a commercial structure, enter your project dimensions and specifications to get a complete rebar materials list. We calculate total bars needed, linear footage, weight in pounds and tons, and lap splice requirements per ACI 318 standards.
Trusted Sources
How to Use the Rebar Calculator
- 1Select your project type: slab, footing, wall, column, or custom grid.
- 2Enter the dimensions (length, width, height/depth as applicable).
- 3Choose your rebar size (#3 through #8 are most common for residential).
- 4Specify the spacing for bars in each direction (on center, OC).
- 5Enter concrete cover thickness (typically 2-3 inches for exterior).
- 6Toggle lap splice calculation to include overlap requirements.
- 7Review total bars, linear footage, weight, and cost estimate.
- 8Print your materials list for ordering from your supplier.
Rebar Size Chart and Specifications
Rebar is designated by numbers indicating eighths of an inch in diameter:
Standard Rebar Sizes (ASTM A615):
| Bar Size | Diameter | Area (sq in) | Weight/Ft | Typical Use |
|---|---|---|---|---|
| #3 | 3/8" (0.375") | 0.11 | 0.376 lb | Slabs, temp steel, light applications |
| #4 | 1/2" (0.500") | 0.20 | 0.668 lb | Slabs, walls, footings |
| #5 | 5/8" (0.625") | 0.31 | 1.043 lb | Footings, walls, beams |
| #6 | 3/4" (0.750") | 0.44 | 1.502 lb | Heavy footings, columns |
| #7 | 7/8" (0.875") | 0.60 | 2.044 lb | Large structural members |
| #8 | 1" (1.000") | 0.79 | 2.670 lb | Commercial, heavy structural |
| #9 | 1-1/8" (1.128") | 1.00 | 3.400 lb | Large commercial |
| #10 | 1-1/4" (1.270") | 1.27 | 4.303 lb | Heavy commercial |
| #11 | 1-3/8" (1.410") | 1.56 | 5.313 lb | Bridge, industrial |
Standard Stock Lengths:
- Most common: 20 feet
- Also available: 30, 40, 60 foot lengths
- Custom cut lengths: Available with minimum orders
Rebar Grades:
| Grade | Yield Strength | Ultimate Strength | Applications |
|---|---|---|---|
| Grade 40 | 40,000 PSI | 60,000 PSI | Light residential, non-structural |
| Grade 60 | 60,000 PSI | 90,000 PSI | Standard (most common) |
| Grade 75 | 75,000 PSI | 100,000 PSI | High-strength applications |
| Grade 80 | 80,000 PSI | 105,000 PSI | Seismic, heavy loads |
Note: Grade 60 is the default assumption for most residential/commercial work and all ACI calculations.
Rebar Spacing Guidelines
Proper spacing ensures adequate reinforcement without overcrowding:
Residential Concrete Slabs:
| Application | Bar Size | Spacing | Cover | Notes |
|---|---|---|---|---|
| 4" patio/walkway | #3 or mesh | 18" OC | 1.5" | Non-structural, light use |
| 4" garage slab | #3 | 18" OC | 2" | Typical residential |
| 5" driveway | #4 | 16" OC | 2" | Vehicle traffic |
| 6" heavy duty | #4 | 12" OC | 2" | RV/heavy equipment |
| 8" commercial | #5 | 12" OC | 2" | Per engineer |
Footings:
| Footing Width | Bar Size | Longitudinal Bars | Transverse |
|---|---|---|---|
| 12" | #4 | 2 bars continuous | None required |
| 16" | #4 | 3 bars continuous | #4 @ 24" OC |
| 20" | #5 | 3 bars continuous | #4 @ 18" OC |
| 24" | #5 | 4 bars continuous | #4 @ 18" OC |
| 30" | #5 | 4-5 bars continuous | #4 @ 16" OC |
| 36"+ | #6 | Per engineer | Per engineer |
Walls:
| Wall Type | Vertical | Horizontal |
|---|---|---|
| Foundation 8" | #4 @ 32" OC | #4 @ 48" OC |
| Foundation 10" | #5 @ 24" OC | #4 @ 32" OC |
| Retaining 8" | #5 @ 24" OC | #4 @ 24" OC |
| Retaining 10" | #5 @ 16" OC | #4 @ 24" OC |
| Retaining 12" | #5 @ 16" OC | #5 @ 24" OC |
Maximum Spacing Rules:
- Slabs: Maximum 18" or 3× slab thickness, whichever is less
- Walls: Maximum 18" for vertical, 12" for horizontal in structural walls
- Footings: Minimum of 2 longitudinal bars in any footing
Lap Splices and Development Length
When rebar must be joined, overlapping (lap splicing) is the most common method:
Lap Splice Requirements (Grade 60, Tension):
| Bar Size | Class A Splice | Class B Splice | Compression |
|---|---|---|---|
| #3 | 12" | 15" | 12" |
| #4 | 15" | 19" | 15" |
| #5 | 19" | 24" | 19" |
| #6 | 23" | 29" | 22" |
| #7 | 32" | 39" | 26" |
| #8 | 36" | 45" | 30" |
| #9 | 41" | 51" | 34" |
| #10 | 46" | 58" | 38" |
Splice Classes (ACI 318):
- Class A: Less than 50% of bars spliced at same location, adequate reinforcement
- Class B: More than 50% of bars spliced at same location (most common condition)
Development Length Formula: Tension: Ld = (fy × db) / (25 × √f'c) × modification factors Simplified rule: Lap splice = 40-60 bar diameters for tension
Lap Splice Best Practices:
- Stagger splices (don't splice all bars at same location)
- Tie splices with wire at both ends and middle
- Minimum 1.5 bar diameters between parallel spliced bars
- Splice in low-stress areas when possible
- Avoid splicing in plastic hinge regions (seismic)
Standard Hooks:
| Hook Type | Bend Angle | Minimum Extension |
|---|---|---|
| Standard 180° | 180 degrees | 4db, then 4db |
| Standard 90° | 90 degrees | 12db minimum |
| Stirrup/Tie 135° | 135 degrees | 6db minimum |
| Stirrup/Tie 90° | 90 degrees | 6db (interior) |
Where "db" = bar diameter
Concrete Cover Requirements
Concrete cover protects rebar from corrosion and provides bond:
Minimum Cover (ACI 318):
| Location | Required Cover |
|---|---|
| Cast directly against earth | 3" |
| Exposed to earth/weather (#6 and larger) | 2" |
| Exposed to earth/weather (#5 and smaller) | 1.5" |
| Not exposed to weather: Slabs/walls | 0.75" |
| Not exposed to weather: Beams/columns | 1.5" |
| Fire-rated construction | Per rating table |
Why Cover Matters:
- Prevents corrosion from moisture penetration
- Provides bond between concrete and steel
- Protects from fire damage
- Inadequate cover = cracking and premature failure
- Too much cover = reduced structural capacity
Placing and Support:
| Bar Size | Maximum Chair Spacing |
|---|---|
| #3-#4 | 4 ft maximum |
| #5-#6 | 3 ft maximum |
| #7-#8 | 2 ft maximum |
| #9+ | 18" maximum |
Support Types:
- Wire chairs (most common)
- Plastic chairs/wheels
- Concrete blocks (dobies)
- High chairs for top steel
- Continuous supports for heavy bars
Special Conditions:
- Marine/coastal: Increase cover by 1"
- Parking garages: Minimum 2" recommended
- Aggressive soils: Consider epoxy-coated rebar
- Freeze-thaw zones: Air-entrained concrete essential
2026 Rebar Pricing Guide
Current pricing for reinforcing steel:
Rebar Prices (per linear foot):
| Bar Size | Supplier Price | Big Box Store |
|---|---|---|
| #3 (3/8") | $0.35-0.50 | $0.50-0.70 |
| #4 (1/2") | $0.55-0.75 | $0.75-1.00 |
| #5 (5/8") | $0.85-1.10 | $1.10-1.40 |
| #6 (3/4") | $1.20-1.50 | $1.50-2.00 |
| #7 (7/8") | $1.70-2.10 | $2.20-2.80 |
| #8 (1") | $2.20-2.80 | $2.80-3.50 |
Bulk Pricing (per ton):
| Grade | Price Range | Notes |
|---|---|---|
| Grade 40 | $800-1,000 | Limited availability |
| Grade 60 | $900-1,200 | Standard pricing |
| Epoxy-coated | $1,400-1,800 | Corrosion protection |
| Stainless | $4,000-6,000 | Marine/bridge applications |
Accessories:
| Item | Unit | Price |
|---|---|---|
| Wire ties (16 ga) | 1 lb coil | $4-6 |
| Bar chairs (wire) | each | $0.25-0.50 |
| Bar chairs (plastic) | each | $0.10-0.25 |
| High chairs (4") | each | $0.75-1.25 |
| Dobies (concrete blocks) | each | $0.50-1.00 |
Cost Examples by Project:
| Project | Rebar Needed | Approx Cost |
|---|---|---|
| 20×20 garage slab (#3@18") | ~750 LF | $300-400 |
| 10×50 driveway (#4@16") | ~1,200 LF | $700-900 |
| 12"×100' footing | ~600 LF #5 | $600-750 |
| 8'×8' foundation wall | ~800 LF #4 | $500-650 |
Cost-Saving Tips:
- Buy by the ton for large projects
- Order standard 20' lengths when possible
- Ask about contractor/volume pricing
- Compare supplier vs. big box prices
Rebar Calculation Methods
Calculate rebar quantities for different applications:
For Slabs (Grid Pattern):
Formula:
- Long direction bars: (Width ÷ Spacing) + 1 × Length
- Short direction bars: (Length ÷ Spacing) + 1 × Width
- Total = sum of both directions
Example: 20'×30' slab with #4 @ 16" OC: Long direction: (20×12)/16 + 1 = 16 bars × 30' = 480 LF Short direction: (30×12)/16 + 1 = 24 bars × 20' = 480 LF Total: 960 linear feet Add 10% for laps: 1,056 LF Weight: 1,056 × 0.668 = 705 lbs
For Footings:
Continuous footings:
- Longitudinal: 2-4 bars × total length + lap splices
- Transverse: Width bars × (length ÷ spacing + 1)
Example: 16" × 80' footing with 3 #5 longitudinal, #4 @ 24" OC transverse: Longitudinal: 3 × 80' = 240 LF (add 40 LF for splices) = 280 LF #5 Transverse: 2' bars × (80/2 + 1) = 2' × 41 = 82 LF #4 Total weight: (280 × 1.043) + (82 × 0.668) = 347 lbs
For Walls:
Formula:
- Vertical: (Length ÷ Spacing + 1) × Height × 2 faces
- Horizontal: (Height ÷ Spacing + 1) × Length × 2 faces
Waste Factors:
- Simple slabs: Add 5-10%
- Complex shapes: Add 10-15%
- Bent bars: Add 15-20%
- Heavy splicing: Add 10% for overlap
Placing and Inspection Requirements
Proper placement ensures structural performance:
Before Concrete Pour:
- Verify bar sizes against plans
- Check spacing with tape measure
- Confirm cover with gauge
- Ensure bars are tied securely
- Remove any rust, oil, or debris
- Check lap splice lengths
- Verify chairs/supports are adequate
Inspection Points (Per IBC):
| Item | Requirement |
|---|---|
| Bar size | Matches plans exactly |
| Bar grade | Mill marks visible and correct |
| Spacing | Within 1" of specified |
| Cover | Within 1/4" of specified |
| Lap splices | Minimum length achieved |
| Tie wire | At every intersection (min 50%) |
| Support | Adequate to prevent displacement |
Common Violations:
- Insufficient concrete cover
- Wrong bar size used
- Bars not tied at intersections
- Inadequate lap splice length
- Rebar touching forms
- Missing chairs/supports
- Rusty or contaminated bars
Documentation Requirements:
- Approved shop drawings
- Mill certificates (commercial work)
- Inspection reports
- Photos of reinforcement before pour
Post-Pour Issues:
- Exposed rebar: Must be cut and patched
- Cracking over bars: May indicate inadequate cover
- Settlement cracks: Possible bar displacement
Special Applications and Considerations
Specific requirements for common applications:
Seismic/High-Risk Zones:
- Closer spacing required
- Special hook details
- Confinement steel in columns
- No splicing in plastic hinge regions
- Grade 60 or higher required
Elevated Slabs/Decks:
- Top and bottom steel required
- Continuous bars over supports
- Special edge reinforcement
- Minimum #4 bars typically
Retaining Walls:
- Main steel on tension (back) face
- Temperature steel on front face
- Vertical bars extend into footing
- Hook at top of wall
Pool Shells:
- #4 @ 12" both directions typical
- 2" cover minimum all surfaces
- Continuous without splices preferred
- Epoxy coating in salt water
Driveways (Heavy Load):
- #4 @ 12" OC both directions
- Minimum 5" slab thickness
- Thickened edges at 8"
- Control joints @ 10' max
Epoxy-Coated Rebar: When to use:
- Bridge decks
- Marine structures
- Parking garages
- Chemically exposed areas
- Corrosive soil conditions
Cost premium: 30-50% over black rebar Installation: Handle carefully (don't damage coating)
Pro Tips
- 💡Buy 10-15% extra rebar to account for lap splices, waste from cutting, and field changes—running short delays concrete pours.
- 💡Keep rebar off the ground and covered to prevent excessive rust before installation—use wood blocks or pallets.
- 💡Use a rebar bender for hooks rather than cutting—cutting creates sharp ends that are dangerous and non-compliant.
- 💡Tie at least every other intersection for slabs; tie every intersection in walls, beams, and columns.
- 💡Mark spacing on forms before placing rebar to ensure consistent coverage throughout the pour.
- 💡Verify bar sizes against plans—bars are marked with a number (3-11) indicating eighths of an inch in diameter.
- 💡Position lap splices in areas of lower stress when possible—middle third of spans, not at supports.
- 💡Use proper chairs and supports—rebar that shifts during the pour ruins the structural design.
- 💡Never substitute smaller bars at closer spacing without engineering approval—it changes the structural behavior.
- 💡For complex projects, request shop drawings showing bar sizes, spacing, and splice locations.
- 💡Check that mill marks are visible and match the required grade—unmarked bars should not be used.
- 💡Document your rebar placement with photos before the pour—inspectors and future owners appreciate the record.
Frequently Asked Questions
Rebar costs approximately $0.35-2.80 per linear foot depending on size. #3 (3/8") costs $0.35-0.70/ft, #4 (1/2") costs $0.55-1.00/ft, #5 (5/8") costs $0.85-1.40/ft, and #6 (3/4") costs $1.20-2.00/ft. Big box stores are typically 25-40% more expensive than steel suppliers. For large projects, buying by the ton ($900-1,200/ton for Grade 60) is more economical.
