Rebar Calculator
Calculate rebar quantity, linear feet and total weight for concrete slabs.
Bars Along Length
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Bars Along Width
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Total Bars
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Total Linear Feet
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Total Weight (lbs)
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How the Rebar Calculator Works
This rebar calculator determines the number of steel bars needed for a concrete slab by computing a two-direction grid. Bars running along the width direction are spaced across the slab length; bars running along the length direction are spaced across the slab width. The number of bars in each direction is the dimension in inches divided by the spacing, rounded up, plus one end bar. Each bar's length includes an overlap allowance for splicing — typically 6 inches minimum. Total linear footage multiplied by the weight per foot (which varies by bar size: #3 through #6) gives the total steel weight. Use this to estimate material costs and delivery needs before ordering.
Frequently Asked Questions
What size rebar do I need for a concrete slab?
#4 rebar (1/2 inch diameter) is standard for residential driveways and slabs. #5 or #6 for heavier loads.
How far apart should rebar be spaced?
12–18 inches on center is typical for residential slabs. High-traffic areas may require 12-inch spacing.
How much does rebar weigh per foot?
#3=0.376 lb/ft, #4=0.668 lb/ft, #5=1.043 lb/ft, #6=1.502 lb/ft.
Do I need rebar for a 4-inch concrete slab?
For most residential uses (patios, driveways), yes. Use #4 at 18-inch spacing. Lightly loaded walkways can use wire mesh instead.