Rebar Spacing Calculator
Calculate rebar spacing, quantity, and total length needed for concrete slabs, walls, and footings.
Rebar (reinforcing bar) strengthens concrete by resisting tension forces. Proper spacing ensures the concrete structure can handle the loads it was designed for.
Rebar spacing formula:
Number of Bars = (Slab Length / Spacing) + 1
This applies in each direction for a grid pattern.
Total rebar length:
Total Length = (Bars in Direction 1 x Slab Width) + (Bars in Direction 2 x Slab Length)
Common rebar sizes:
| Size | Diameter | Weight per foot |
|---|---|---|
| #3 | 3/8 inch (9.5 mm) | 0.376 lb (0.17 kg) |
| #4 | 1/2 inch (12.7 mm) | 0.668 lb (0.30 kg) |
| #5 | 5/8 inch (15.9 mm) | 1.043 lb (0.47 kg) |
| #6 | 3/4 inch (19.1 mm) | 1.502 lb (0.68 kg) |
Typical spacing guidelines:
- Residential slabs: 12-18 inches (30-45 cm) on center.
- Driveways and garage floors: 12 inches (30 cm) on center.
- Foundation walls: 12 inches (30 cm) horizontal, 12-16 inches (30-40 cm) vertical.
- Footings: 6-12 inches (15-30 cm) on center.
Overlap requirement: Where bars need to be joined, overlap by at least 40 bar diameters. For #4 rebar, that means 20 inches (50 cm) of overlap.
Always follow your local building codes and engineering specifications for structural applications.