How this calculator works
It lays out a grid of rebar at your chosen spacing in both directions, totals the linear feet, and divides by your bar length to get how many bars to buy.
Worked example — a 20 ft × 12 ft slab, 16 in grid, 20 ft bars:
≈400 linear feet of rebar → 20 bars.
≈400 linear feet of rebar → 20 bars.
Don’t forget overlap
Where bars meet end-to-end they must overlap (about 40× the bar diameter). For long runs, add a bit extra for these laps.
Frequently asked questions
What spacing should rebar be in a slab?
A 12–18 inch grid is common for residential slabs; check your project’s requirements.
How much rebar for a 20×12 slab?
About 400 linear feet on a 16-inch grid — roughly 20 bars of 20 ft.