Concrete Slab Calculator
Yards and bags for a patio, shed base, or driveway slab?
How this is calculated
- Volume = length × width × (thickness ÷ 12) in cubic feet
- Cubic yards = volume ÷ 27, plus the waste allowance
- Bags = ⌈volume × 27 ÷ 0.6⌉ at 80 lb per bag (hand-mixing option)
Common questions
How much concrete for a 10×10 slab?
At the standard 4-inch patio thickness: 1.23 cubic yards, order 1.36 with waste. At 6 inches (driveway spec): 1.85 yards, order 2.04. The thickness change alone is 50% more concrete — pick the spec before you price the pour.
How thick should a concrete slab be?
Patios, walkways, shed pads: 4 inches. Residential driveways: 5-6 inches over 4-6 inches of compacted gravel, with rebar or fiber mesh. Garage floors: 5-6 inches. The base under the slab matters as much as the thickness — concrete on un-compacted fill cracks no matter how thick it is.
Do I need rebar or wire mesh in my slab?
Wire mesh or fiber: standard for 4-inch patios and walks — it holds cracks tight rather than preventing them. Rebar (#3 at 18-24 in grid): driveways, anything vehicles cross, and slabs on questionable fill. Control joints every 8-10 ft (sawed or tooled within the first day) do more for crack control than any reinforcement.
Bags or ready-mix for my slab?
Under ~1 yard (45 bags), bags are viable with a mixer and a helper. Above that, ready-mix wins on price ($150-250/yd³ vs $270+ bagged) AND on quality — a truck pours the whole slab in minutes, while bag-mixing a 2-yard pour means cold joints where one section cured before the next arrived.
What is the base under a concrete slab?
4-6 inches of compacted crushed stone (#57 or crusher run) over leveled, compacted subgrade — never pour on bare soil or fresh fill. The base drains, supports the slab evenly, and stops the freeze-thaw pumping that turns bare-ground slabs into cracked wreckage within a few winters.