Calculate ready-mix concrete yardage, gravel base tonnage, and rebar reinforcement grid sticks for slabs, patios, and garage floors.
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A concrete slab calculator models complete structural ground slabs for patios, driveways, garages, and shed foundations. Beyond basic concrete yardage, it calculates the underlying crushed gravel subbase, #4 rebar grid sticks (at 12" or 18" on-center), and ready-mix truckload cycles.
V_{\text{slab}} = \frac{L \times W \times (T / 12)}{27} \times 1.10, \quad \text{Rebar Sticks} = \left\lceil \frac{(N_L \times L + N_W \times W) \times 1.10}{20} \right\rceilIncludes 10% concrete contingency, 15% gravel compaction loss, and 10% rebar overlap splices.
Scenario: Pouring a 24 ft by 24 ft two-car garage slab, 4 inches thick, with 4 inches of gravel base and #4 rebar @ 18" OC.
Concrete volume: 576 sq ft × 0.333 ft ÷ 27 = 7.11 cu yds (+ 10% = 7.82 cu yds).
Gravel subbase: 7.11 cu yds × 1.15 compaction × 1.4 tons/yd = 11.45 tons.
Rebar grid (#4 20-ft sticks): 43 sticks.
Standard residential patio slabs and walkways should be 4 inches thick. If the slab will support hot tubs, heavy storage sheds, or vehicle traffic, pour at 5 to 6 inches thick.
While plain concrete can carry light foot traffic, adding #4 (1/2") rebar or 6x6 welded wire mesh prevents cracked segments from separating and shifting over time.
A 10 ft by 10 ft slab at 4 inches thick requires approximately 1.35 cubic yards of concrete, which equals about 62 eighty-pound bags or 82 sixty-pound bags.
You can walk on a fresh slab after 24 to 48 hours and begin wooden wall framing after 7 days (when concrete reaches ~70% strength). Full cure is 28 days.
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Area: 576 sq ft | ~0.8 Ready-Mix Truckloads (10-yd)