Free Rebar Spacing Calculator
Calculate rebar spacing, number of bars, and layout for slabs, walls, and footings. Determine bar counts for a given spacing.
Min concrete cover from edge to first bar
Number of Bars
30
Number of Bars vs Span Length
How to Calculate Rebar Spacing
Formula
Usable Span = Total Span - 2 × Edge Cover
Number of Bars = floor(Usable Span / Spacing) + 1
Actual Spacing = Usable Span / (Number of Spaces) × 12
Edge cover is the minimum distance from the edge of the concrete to the nearest rebar. Typical cover is 3 inches for cast-against-ground concrete and 1.5 inches for formed surfaces.
Example Calculation
Rebar across a 30 ft span at 12-inch spacing with 3-inch edge cover.
- 01Cover in feet = 3 / 12 = 0.25 ft
- 02Usable span = 30 - 2 × 0.25 = 29.5 ft
- 03Spacing in feet = 12 / 12 = 1.0 ft
- 04Number of bars = floor(29.5 / 1.0) + 1 = 30 bars
- 05Actual spacing = 29.5 / 29 × 12 = 12.21 inches
Frequently Asked Questions
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