Rebar Spacing Calculator

Calculate rebar quantity, spacing, and layout for concrete slabs, footings, and walls. Determine number of bars, total linear feet, and weight.

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Rebar sizes go by bar number: #3 = 3/8 inch, #4 = 1/2 inch, #5 = 5/8 inch, #6 = 3/4 inch diameter. For residential slabs, #3 or #4 at 12-18 inches on center is typical. Rebar should be placed at 1/3 from the bottom of the slab, supported by chairs or dobies. Overlap (lap splice) should be at least 40 bar diameters, that is 20 inches for #4 bars. Wire mesh (6x6 W2.9xW2.9) is an alternative for light-duty slabs.