🔩 Rebar Calculator PRO
Professional steel reinforcement calculator — slabs, columns, beams, footings. Bar schedules, lap splices, wire ties, and cost per ACI 318.
Slab Rebar Grid — updates as you type
Two-way bar layout at the set spacing. Steel weight follows bar count times length.
1 Layout Type
2 Dimensions
2 Column Dimensions
2 Beam Dimensions
3 Rebar Settings
4 Cost & Details
Labour Cost
Results
Bar Counts
Weights & Schedule
Costs
Bar Bending Schedule
| Type | Qty | Length | Shape |
|---|---|---|---|
Material Breakdown by Size
⚠️ Pre-Export Checklist
- Dimensions verified from structural drawings
- Rebar size and spacing per engineer's specification
- Concrete cover maintained per exposure condition
- Lap splices specified (Class A or B per ACI 318)
- Chairs/bolsters for proper rebar elevation
- Temperature and shrinkage steel included where required
- 10% extra for waste, bends, and field adjustments
Rebar Reference & Professional Guide
Show bar size table, formulas, and worked examples ▼
Rebar Size Reference Table
| Size | Diameter | Area (in²) | Weight (lb/ft) | Typical Use |
|---|---|---|---|---|
| #3 | 3/8" | 0.11 | 0.376 | Light slabs, driveways, stirrups |
| #4 | 1/2" | 0.20 | 0.668 | Residential slabs, footings |
| #5 | 5/8" | 0.31 | 1.043 | Structural slabs, walls |
| #6 | 3/4" | 0.44 | 1.502 | Heavy foundations |
| #7 | 7/8" | 0.60 | 2.044 | Commercial footings, columns |
| #8 | 1" | 0.79 | 2.670 | Heavy commercial, bridge decks |
| #9 | 1-1/8" | 1.00 | 3.400 | Columns, transfer beams |
| #10 | 1-1/4" | 1.27 | 4.303 | High-rise columns, piers |
| #11 | 1-3/8" | 1.56 | 5.313 | Bridge piers, foundations |
ACI 318 Formulas
Bars (one direction)= (Dimension perpendicular to bars ÷ Spacing) + 1
Total Linear Feet= (Bars in A × Length A) + (Bars in B × Length B)
Weight= Total Linear Feet × Weight per Foot (lb/ft)
Lap Splice (Class A)= 40 × bar diameter (min overlap)
Lap Splice (Class B) = 48 × bar diameter (required when >50% spliced)
Temp & Shrinkage Steel (fy=60,000)= 0.0018 × b × h (ACI 318 §24.4.3.2)
Column Tie Spacing= min(16× long. bar dia, 48× tie dia, column dim)
Wire Tie Length = Perimeter + 2 × hook allowance (approx. 6" per tie for #3 ties)
Worked Example — Grid Slab
20 ft × 12 ft slab, #4 rebar at 12" spacing, no overlay:
- Bars along length: (12 ÷ 1) + 1 = 13 bars (each 20 ft long)
- Bars along width: (20 ÷ 1) + 1 = 21 bars (each 12 ft long)
- Total bars: 13 + 21 = 34 bars
- Linear feet: (13 × 20) + (21 × 12) = 260 + 252 = 512 ft
- Weight: 512 × 0.668 = 342 lbs
- Ties: 13 × 21 = 273 ties (2× wire per tie = 546 wire ties)
- Lap splices (48× dia for #4 = 24"): estimated 4 extra bars per direction
Concrete Cover Requirements
- 1.5" — Interior (cast against ground not included)
- 2" — Exterior (exposed to weather or in contact with ground)
- 3" — Buried (concrete cast against and permanently exposed to earth)
Common Mistakes to Avoid
- Using wrong weight per foot — #4 and #5 look similar but differ 56%
- Forgetting overlay doubles all quantities
- Not accounting for lap splices (add 40-48× diameter per splice)
- Ignoring concrete cover — rebar must be elevated on chairs
- Omitting temperature and shrinkage steel in slabs on grade
Tips
- #4 is the most common for residential slabs (4" thick)
- Use 12" spacing for standard slabs, 6" for heavy loads
- Always order 10% extra for lap splices, waste, and bends
- Wire ties: 2 ties per intersection, 6" wire per tie minimum
- Chairs every 2-3 ft in both directions to maintain cover
Related Calculators
Frequently used together on the same project.
Client & Quote (prints on PDF & Excel)
Adjustments (applies to exports)
Contingency is added as a separate line on the exported cost summary. Waste % is printed as an advisory reminder.
Project notes (prints on PDF & Excel)
Result compare (A/B)
| Item | Pinned | Current | Change |
|---|---|---|---|
Saved rates auto-apply from your Price Library. Advanced details stay in your browser — nothing is uploaded except inside your own PDF/Excel exports.
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Maintained by theBuildingCalc methods desk· Last reviewedSeptember 23, 2026. This calculator implements the standards and references below; every figure can be rechecked against the formulas and worked example on this page.
Results are estimates, not engineering advice. Verify against local codes and licensed professionals for structural, electrical, and gas work. See ourTerms. Spotted an error? Report it— corrections ship with the next review.