Rebar Grid Calculator
Determine rebar bar counts, total linear footage, lap splices, and steel tonnage for reinforced concrete slabs.
Recommended Tools & Equipment
Tested hardware and components for high reliability
How Rebar Grid Spacing and Weight Work
Concrete has enormous compressive strength but poor tensile strength. Deformed steel rebar carries the tensile loads, preventing concrete slabs from pulling apart when subsoil shifts or heavy vehicle tires traverse over top.
Standard US bar numbering represents nominal bar diameter in eighths of an inch:
- #3 Rebar: 3/8" diameter (0.376 lbs per linear foot)
- #4 Rebar: 4/8" = 1/2" diameter (0.668 lbs per linear foot)
- #5 Rebar: 5/8" diameter (1.043 lbs per linear foot)
- #6 Rebar: 6/8" = 3/4" diameter (1.502 lbs per linear foot)
Frequently Asked Questions
Should rebar sit on the ground during a concrete pour?
Never. Rebar sitting on the ground provides zero tensile strength. Support rebar grids on plastic concrete dobies or rebar chairs at the center-to-lower third of the slab depth.
How far apart should rebar be in a driveway slab?
Residential driveways typically specify #4 rebar on an 18" x 18" grid, or 12" x 12" grid for heavy truck parking or poor expansive clay soils.
What is the required lap splice for #4 rebar?
At 30 bar diameters: 30 × 0.5 inches = 15 inches minimum overlap where bars meet.