Rebar Calculator

For a typical residential slab, bars on a 12-inch grid (both directions) is common, sometimes opening to 16 or 18 inches for light-duty pours like a small patio. Heavier loads, footings, and structural slabs tighten the spacing. Match the spacing to your plan or local code, then enter it here.

Rebar comes in stock lengths (often 20 feet), so on a run longer than one bar you overlap two bars and tie them so loads transfer across the joint. A common lap is 40 bar-diameters — roughly 12 inches for #3 and 18+ inches for larger bars. The tool adds that overlap so your linear-foot total reflects the real material used.

Edge clearance (concrete cover) is the gap between the outermost bar and the edge of the slab. It keeps steel embedded in concrete so it does not rust or break out at the surface — usually about 3 inches from earth-cast edges and less for formed faces. Setting it correctly slightly shortens each bar in the grid.

#3 bar (3/8 inch) is common for residential slabs and #4 (1/2 inch) for footings and heavier slabs; larger structures step up from there. This calculator gives you linear feet regardless of size, so pick the bar your plan calls for and order that many stock lengths.

Divide the total linear feet by your stock length — usually 20 feet per bar — and round up. Account for the laps already included and add a few extra bars for miscuts and corner bends. Buying a couple of spare sticks is cheaper than stopping the pour to fetch more.

Simply type your numbers and read the result, which refreshes the instant you change something. There is nothing to submit and nothing to wait for.

Not at all — it runs in the browser with nothing to install and no account. After it loads once, it even works without an internet connection.

Yes. Everything happens in your browser. Nothing you type is sent to a server or saved anywhere.