How to Calculate Rebar for a Slab
Bars per direction: (Slab dimension in inches / Spacing) + 1
Linear feet per direction: Bars x Slab dimension perpendicular
Weight: Total linear feet x Weight per foot for bar size
Rebar Weight Per Foot by Size
- #3 (3/8") - 0.376 lb/ft
- #4 (1/2") - 0.668 lb/ft
- #5 (5/8") - 1.043 lb/ft
- #6 (3/4") - 1.502 lb/ft
- #7 (7/8") - 2.044 lb/ft
- #8 (1") - 2.670 lb/ft
Frequently Asked Questions
What spacing should I use? 12" on center is standard for residential slabs. Use 6" for heavy-duty applications like driveways.
How much overlap is needed? Standard overlap (lap splice) is 24-30 bar diameters, typically 24" minimum for #4 bars.