How much rebar do I need?
Estimate the total length of rebar and number of 40-ft sticks for concrete slabs based on slab dimensions and spacing.
Rebar calculator
Choosing the Right Rebar
Rebar grade and size determine the structural strength of reinforced concrete. Selecting the correct reinforcement is critical for load-bearing slabs, footings, and walls.
Grade 40 Rebar: Minimum yield strength of 40,000 psi. Suitable for light residential work including small slabs, walkways, patios, and non-structural walls. Most economical option for basic reinforcement.
Grade 60 Rebar: Yield strength of 60,000 psi. The standard for most residential and commercial construction. Used for footings, foundation walls, driveways, and structural slabs. Offers the best balance of strength and cost.
Grade 80 Rebar: High-strength reinforcement (80,000 psi) for heavy-duty applications. Used in high-rise buildings, bridges, retaining walls, and industrial floors. Requires more careful placement and inspection.
Epoxy-Coated Rebar: Standard steel rebar with an epoxy coating for corrosion resistance. Essential for structures exposed to de-icing salts, marine environments, or high moisture. More expensive but significantly extends service life.
Rebar Grade Cheat Sheet
Use this reference to select the right rebar for your project:
| Grade | Strength (psi) | Best Used For |
|---|---|---|
| Grade 40 | 40,000 | Light residential slabs, walkways, patios, non-structural walls |
| Grade 60 | 60,000 | Footings, foundations, driveways, structural slabs, beams |
| Grade 80 | 80,000 | High-rises, bridges, retaining walls, industrial floors |
| Epoxy-Coated | 40,000–60,000 | Marine environments, bridges, salt-exposed structures |
Rebar placement guidelines
- Slab on grade: Use #3 or #4 rebar at 12-18 inches spacing
- Driveways: #4 rebar at 12-18 inches
- Footings: #4 or #5 rebar, 2-4 continuous bars
- Retaining walls: #4 or #5 rebar at 12-24 inches
Rebar should be placed in the middle third of the slab thickness. Use wire chairs or rebar supports to hold it at the correct height during the pour.
Worked example
For example, for a 10×8 ft slab, #4 rebar at 12-in spacing:
- Horizontal bars: (8 × 12 ÷ 12) + 1 = 9 bars at 10 ft = 90 ft
- Vertical bars: (10 × 12 ÷ 12) + 1 = 11 bars at 8 ft = 88 ft
- Total length = 90 + 88 = 178 ft
- 40-ft sticks needed = 178 ÷ 40 = 4.45 → 5 sticks
- Add 10% for overlaps and bends: 5 × 1.10 = 6 sticks
Common mistakes
| Mistake | Why it matters |
|---|---|
| Using bars that are too far apart | Maximum spacing is typically 18 in — 12 in is better for most residential slabs |
| Not supporting bars off the ground | Use rebar chairs or dobies to keep rebar in the middle of the slab |
| Forgetting to overlap at splices | Overlap bars by at least 40 bar diameters (20 in for #4) at joints |