Rebar Calculator
Grid pattern for slabs & walls
Standard lengths: 20, 30, 40 ft
Typ. 1 ft for #4, more for larger
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Rebar size reference
| Bar No. | Diameter | Weight (lb/ft) | Common use |
|---|---|---|---|
| #3 | 3/8" | 0.376 | Light slabs, driveways |
| #4 | 1/2" | 0.668 | Most residential slabs |
| #5 | 5/8" | 1.043 | Walls, heavy slabs |
| #6 | 3/4" | 1.502 | Columns, foundations |
| #7 | 7/8" | 2.044 | Heavy foundations |
| #8 | 1" | 2.670 | Commercial structures |
Rebar FAQ
What size rebar do I need for a concrete slab?
#4 rebar (1/2" diameter) at 12-inch spacing is standard for most residential slabs like patios, driveways, and floors. For heavier loads or thicker slabs (6"+), use #5 rebar at 12-inch spacing. Driveways with heavy vehicles benefit from #4 at 6-inch spacing.
Do I need rebar in a concrete slab?
Rebar significantly improves the tensile strength of concrete, which is weak in tension. For slabs thicker than 4" or any slab bearing vehicle loads, rebar is strongly recommended. Small decorative slabs or sidewalks may use wire mesh instead for economy.
How much does rebar cost?
#4 rebar costs approximately $0.40–$0.65 per linear foot, or $8–$13 per 20-foot bar. Prices fluctuate with steel markets. Buying in bundle quantities from steel suppliers is typically 15–25% cheaper than buying individual bars from home improvement stores.