Rebar Calculator
Calculate rebar needed for concrete slabs and footings. Get total bars, linear feet, and weight by bar size (#3โ#8) and spacing.
๐ฉ Rebar Calculator
Results
Bars (lengthwise)21 bars
Bars (widthwise)21 bars
Total Bars42 bars
Total Linear Feet840.00 ft
Total Weight561.1 lbs
๐ก How to Calculate Rebar Quantities
Rebar is placed in a grid pattern within concrete to provide tensile strength. Standard residential slab spacing is 12โ18 inches on center (OC) in both directions. Calculate bars in each direction: divide the perpendicular dimension by the spacing and add 1 for the starting bar.
Rebar is identified by bar size number โ the number represents eighths of an inch in diameter. #4 rebar (ยฝ inch) is the most common for residential work. It weighs 0.668 lbs per foot. #3 (โ inch) is used for light-duty, while #5 and #6 are for heavier structural applications.
A 20ร20 ft slab with #4 rebar at 12" OC needs: 21 bars each way = 42 total bars. Total linear feet = 42 ร 20 = 840 ft. Weight = 840 ร 0.668 = 561 lbs of rebar.