Free Rebar Calculator
Calculate Rebar Quantity & Length for Concrete Slabs
Standard: 12″ OC for driveways, 18″ OC for patios
📋 How to Calculate Rebar
Formula: Lengthwise bars = (Width × 12 ÷ Spacing) + 1. Widthwise bars = (Length × 12 ÷ Spacing) + 1.
❓ Rebar Calculator FAQ
How to calculate rebar for concrete slab?
Divide slab width by spacing for lengthwise bars. Divide length by spacing for widthwise bars. Total = (bars × length) + (bars × width).
What is standard rebar spacing?
Standard spacing is 12 to 18 inches on center. Driveways: 12″. Patios: 18″. Commercial: 6-12″.
What size rebar for 4 inch slab?
Use #3 (3/8″) or #4 (1/2″) rebar. #4 is most common for driveways and garage slabs.
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