Rebar Calculator
Calculate how many rebar bars you need for any concrete slab, footing, or column. Get total linear feet, weight, and cost estimate based on rebar size and spacing.
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Extended More scenarios, charts & detailed breakdown ▾
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Total Bars
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Total Linear Feet —
Bars Lengthwise —
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Professional Full parameters & maximum detail ▾
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Rebar Grid
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Weight & Splices
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Hardware & Cost
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How to Use This Calculator
- Enter the slab length and width in feet.
- Enter the rebar spacing in inches (default 12).
- Results show bars needed in each direction, total bars, and total linear feet.
Formula
Bars lengthwise = ceil(Width ÷ Spacing) + 1
Bars widthwise = ceil(Length ÷ Spacing) + 1
Total linear feet = (Bars lengthwise × Length) + (Bars widthwise × Width)
Example
Example: 20×12 ft slab, 12 in spacing → 13 lengthwise + 21 widthwise = 34 bars → 412 linear feet.
Frequently Asked Questions
- For a typical 4-inch residential slab, place #3 or #4 rebar in a 12-inch grid. Calculate bars by dividing each dimension by spacing and adding one. Total linear feet = total bars × their respective lengths.
- Residential slabs: 12–18 inch spacing. Structural slabs and driveways: 12 inches. Footings: 12–18 inches between longitudinal bars. Consult a structural engineer for load-bearing applications.
- #3 rebar weighs 0.376 lbs/ft, #4 = 0.668 lbs/ft, #5 = 1.043 lbs/ft, #6 = 1.502 lbs/ft. Total weight = total linear feet × weight per foot.
- When splicing rebar, the overlap (lap splice) must be at least 40 bar diameters. For #4 rebar (0.5 inch diameter), that is 20 inches minimum.
- #3 (3/8") for light slabs and footings. #4 (1/2") for driveways and most residential slabs. #5 (5/8") and larger for structural applications, retaining walls, and heavy loads.