Concrete is different from every other calculator on this site: it's a manufactured product, not a quarried or organic one, so the question isn't really "how dense is this material" but "how much do I order, and do I mix it myself or call a ready-mix truck." This calculator converts your slab's area and thickness into cubic yards, cubic feet, and tons, using density figures from a major ready-mix producer and the governing structural standard rather than a rounded-off average. Enter the length and width of your slab, pick a thickness — or tap a preset for a patio, a driveway, or a heavy-duty pour — and the results update as you type. Add a price per yard or ton for an estimated cost range. Whether you're bagging a small walkway or ordering a full truck for a driveway, the numbers below are the ones to bring to the supplier.
Enter your dimensions above to see results.
The calculator first finds the volume of the slab in cubic feet: length (ft) × width (ft) × thickness (in ÷ 12). That's converted to cubic yards by dividing by 27, since a cubic yard is 3 ft × 3 ft × 3 ft. A waste percentage is added on top to cover over-excavation and form loss, and the adjusted cubic yardage is multiplied by concrete's density (tons per cubic yard) to get the weight in tons. Bag counts divide the adjusted cubic feet by each bag's yield; ready-mix truckloads divide the adjusted cubic yards by the truck's capacity.
A 10 ft × 10 ft patio slab at 4 inches thick: volume = 10 × 10 × (4 ÷ 12) = 33.33 cubic feet. In cubic yards, that's 33.33 ÷ 27 = 1.23 yd³. Adding a 10% waste factor: 1.23 × 1.10 = 1.36 yd³. At 2.02 tons per cubic yard, that's 1.36 × 2.02 = 2.74 tons — or 2.65–2.76 tons across the full 1.95–2.03 density range. In 80 lb bags, the adjusted 36.67 cu ft (33.33 × 1.10) would need 62 bags — well past the roughly half-cubic-yard point where ready-mix delivery starts making more sense than mixing bag after bag by hand.
Slab thickness is driven almost entirely by what's going to be on top of it, not by preference. 4 inches is the standard for patios, walkways, and other slabs that only need to carry foot traffic — thinner than that and the slab becomes prone to cracking under normal use. 5 to 6 inches is the range for driveways and anything that will carry vehicles, since the slab needs to resist point loads from tires without flexing or cracking; go toward 6 inches if the driveway will see trucks, RVs, or other heavy vehicles regularly. Whatever the thickness, a slab poured directly onto undisturbed or ungraded soil is asking for trouble — a compacted gravel or crushed-stone base underneath gives the slab a stable, well-drained foundation and is standard practice even for a small patio.
Unlike the landscape materials on this site, concrete is a manufactured product with a tightly controlled mix, so its density varies far less than gravel, sand, or mulch. CEMEX, a major ready-mix producer, puts a solid unbroken slab at about two tons (4,000 lbs) per cubic yard, and says one cubic yard takes roughly 45 eighty-pound bags or 90 forty-pound bags. ACI 318 and ASTM C138 define normal-weight concrete at 145–150 lb/ft³ — ACI 318 uses 150 lb/ft³ as its default structural value — which works out to 3,915–4,050 lbs (1.96–2.03 tons) per cubic yard. The 1.95–2.03 ton/yd³ range here reflects that normal-weight span, not moisture variation. Lightweight and heavyweight concrete mixes fall outside this range and aren't covered by this calculator. We use 2.02 tons/yd³ as the display figure, drawn from:
Read more in our density methodology.