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Studs for a wall.
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Construction
Rebar Calculator
Find the bars and linear feet of rebar for a slab.
Total rebar
—
Linear feet.
| Total bars | — |
|---|---|
| Lengthwise bars | — |
| Widthwise bars | — |
| Grid area | — |
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Enter your figures above to see the step-by-step working.
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How the Rebar Calculator Works
For a reinforced slab, rebar is laid in a grid at a set spacing. This calculator counts the bars in each direction — the number of bars equals the slab dimension divided by the spacing, plus one for the starting bar — then adds up the total linear feet you’ll need to buy. A 20×10 ft slab on 12-inch centers needs about 430 linear feet of rebar.
Add a little for overlaps at splices (typically 40 bar diameters) and order the next standard length up. Spacing and bar size come from your slab’s engineering spec.
bars = (dimension × 12 ÷ spacing) + 1, each way
Frequently Asked Questions
How much rebar do I need for a slab?
Count the bars each way (slab size ÷ spacing, plus one) and multiply by the run length. A 20×10 ft slab at 12-inch spacing is about 430 linear feet.
What spacing should rebar be?
Commonly 12–18 inches on center for slabs, but follow your engineering plans.
Should I add extra for overlaps?
Yes — splices overlap about 40 bar diameters, so add a bit and round up to standard lengths.
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