How much rebar do I need?

Lay out a grid at your chosen spacing: the calculator counts the bars in each direction (including the edges), totals the linear feet, and divides by your bar length.

What spacing should rebar be?

For residential slabs, 12–18 inches on center is common. Always check your project drawings or local building code.

How long are rebar sticks?

Standard rebar comes in 20-foot lengths, with 10 and 40 foot also available. The calculator divides the total length by your bar length and rounds up.

Rebar Calculator

Work out how much rebar a slab needs. Enter the slab size and grid spacing to get the total linear feet, the number of bars in each direction, and how many standard bars to buy.

Rebar calculator

Counts a two-way grid at your spacing on-center, including a bar at each edge. Add extra for overlaps at splices (typically 40× the bar diameter). Check your project or local code for spacing.

How it's calculated

We place bars at your spacing on-center in both directions, including a bar at each edge — so the count across a span is floor(span ÷ spacing) + 1. We total the linear feet (bars × their length in each direction) and divide by your bar length, rounding up. Add extra for splice overlaps.

Frequently asked questions

How much rebar do I need?: Lay out a grid at your chosen spacing: the calculator counts the bars in each direction (including the edges), totals the linear feet, and divides by your bar length.
What spacing should rebar be?: For residential slabs, 12–18 inches on center is common. Always check your project drawings or local building code.
How long are rebar sticks?: Standard rebar comes in 20-foot lengths, with 10 and 40 foot also available. The calculator divides the total length by your bar length and rounds up.

Embed this calculator

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<iframe id="hmc-rebar-calculator" src="https://howmanycalc.com/embed/rebar-calculator/" title="Rebar calculator by HowManyCalc" width="100%" height="520" style="border:1px solid #e4e8ec;border-radius:12px;max-width:680px" loading="lazy"></iframe>
<p style="font:12px sans-serif">Rebar calculator by <a href="https://howmanycalc.com/rebar-calculator/">HowManyCalc</a></p>
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Last updated June 2026.