Patio preset — 4 in slab · #4 @ 18 in OC typical
4 in thick, #4 @ 18 in OC.
6 in thick, #4 @ 12 in OC.
20×40 ft, 5 in, #4 @ 12 in.
40×30 ft, 8 in, #5 @ 12 in.
Volume math matches our concrete volume calculator. Reinforcement grid matches slab rebar calculator logic with effective cover.
No. It is a planning calculator for quantity and weight. Bar size, spacing, and thickness must meet approved drawings.
Bag count uses 80 lb yield by default for comparison. Most large slabs order ready-mix by the yard instead.
Concrete cost = cubic yards with waste × your $/yd entry. Steel cost is not included—add material quotes from your supplier.
This tool uses one spacing value both ways. Asymmetric grids need manual adjustment or engineering takeoff.
How we built this calculator: results use the standard volume, area, and coverage formulas shown on this page, with typical U.S. material densities, bag yields, and waste factors that you can override. Written and checked by the YardsCalculator editorial team. Last reviewed: October 2026.
Last updated: May 22, 2026