Rebar Calculator

Calculate rebar needed for concrete slabs and footings. Get total bars, linear feet, and weight by bar size (#3–#8) and spacing.

πŸ”© Rebar Calculator

Results

Bars (lengthwise)21 bars
Bars (widthwise)21 bars
Total Bars42 bars
Total Linear Feet840.00 ft
Total Weight561.1 lbs

πŸ’‘ How to Calculate Rebar Quantities

Rebar is placed in a grid pattern within concrete to provide tensile strength. Standard residential slab spacing is 12–18 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 β€” the number represents eighths of an inch in diameter. #4 rebar (Β½ inch) is the most common for residential work. It weighs 0.668 lbs per foot. #3 (β…œ inch) is used for light-duty, while #5 and #6 are for heavier structural applications.

A 20Γ—20 ft slab with #4 rebar at 12" OC needs: 21 bars each way = 42 total bars. Total linear feet = 42 Γ— 20 = 840 ft. Weight = 840 Γ— 0.668 = 561 lbs of rebar.

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