How it works
Calculate your material requirement
Estimate concrete, gravel base, rebar, form boards, and vapor barrier for a rectangular concrete slab.
The formula
Concrete and base volumes use length × width × depth. Rebar length estimates a two-way grid at the selected on-center spacing; forms use the slab perimeter.
Worked example
A 20 ft × 12 ft slab, 4 in thick, with a 4 in base and 18 in rebar spacing needs about 3.26 yd³ of concrete after a 10% allowance, plus base stone, reinforcing grid, forms, and vapor barrier.
Before you order
- Confirm reinforcement size and spacing with the project design.
- Base depth and compaction requirements depend on soil and drainage.
- Lap lengths, chairs, thickened edges, footings, and penetrations are not included.