Rebar (reinforcing bar) is ridged steel bar used to reinforce concrete structures. Concrete handles compression well but cracks under tension — rebar resists those tensile forces.
Common Sizes (US)
- #3: 3/8" diameter (0.375") — residential slabs
- #4: 1/2" — driveways, footings
- #5: 5/8" — foundations, columns
- #6-#8: Commercial and structural applications
Spacing
Typical spacing: 12"–18" on center for slabs, 6"–12" for walls and footings. Always check local building codes.
Rebar Grade and Strength
Rebar is classified by yield strength: Grade 40 (40,000 psi) is common for light residential use, while Grade 60 (60,000 psi) is standard for most structural and commercial applications today. Higher grades allow the same load-bearing capacity with less steel, but cost more per bar — engineers specify grade based on the structural load calculations, not just size.
Epoxy-Coated and Galvanized Rebar
In coastal or high-moisture environments where corrosion is a concern, epoxy-coated (green) or galvanized rebar resists rust far longer than standard black rebar — critical in structures like bridges and seawalls where steel corrosion has historically caused major, expensive structural failures.