Enter your slab size and bar spacing to get the bars in each direction, the total steel length, and how many stock bars to buy.
This rebar calculator estimates the reinforcement steel for a concrete slab laid as a grid. In each direction it takes the slab size, subtracts the edge cover, divides by the bar spacing and adds one to count the bars; each bar runs the full slab length or width. Adding both directions gives the total length of steel, which it then divides by your stock bar length to tell you how many bars to order.
Bar size, spacing, cover and lap lengths should come from the structural drawing or engineer — reinforcement is a safety-critical detail. This tool is a quick material estimate for ordering and budgeting, not a structural design. Add extra for laps and offcuts on longer spans.
Related: Concrete Calculator · Metal Weight Calculator