Rebar Calculator
Find the rebar grid, weight & cost for your slab
Frequently Asked Questions
Bars each way = (slab dimension − 2× edge clearance) ÷ bar spacing, rounded down, plus 1. Multiply lengthwise and widthwise bar counts by the grid dimensions to get total steel length.
#4 rebar (1/2 inch / 13mm diameter) is the standard choice for slabs on grade like driveways and patios.
It depends on bar size — a #4 bar weighs about 0.668 lb per foot, while a #8 bar weighs about 2.67 lb per foot, per ASTM standard bar weights.
10% is a common allowance for lap splices (where bars overlap and tie together) and cut offcuts.