Construction
Rebar Calculator
Lay out a rebar grid for a concrete slab. Pick spacing, get bar count, total linear feet, and lap-splice allowance.
Enter the slab dimensions.
FAQ
What's the difference between #3, #4, #5? +
The number is the bar diameter in eighths of an inch. #4 = 4/8 = 1/2". For residential slabs, #4 at 16" o.c. is the workhorse.
Why 40× bar diameter for lap splice? +
ACI Code requires roughly 30–50× bar diameter for tension splices depending on conditions. 40× is a safe rule of thumb for slabs-on-grade.
Do I need rebar in a residential slab? +
Concrete cracks. Rebar (or fiber mesh) holds the cracks tight. For driveways and garage slabs, rebar is highly recommended.