How much area does a yard of concrete cover?
By ConcreteLab · Published June 10, 2026 · Updated June 10, 2026
One cubic yard of concrete is exactly 27 cubic feet, so its coverage is 324 ÷ thickness-in-inches square feet: 81 square feet at a 4-inch depth, 64.8 square feet at 5 inches, and 54 square feet at 6 inches — before any waste factor.
Why the answer depends entirely on thickness
"A yard of concrete" is a volume, not an area — one cubic yard is a 3 × 3 × 3 ft cube, exactly 27 cubic feet — so the area it covers depends on how thick you spread it. Pour it thin and it goes far; pour it thick and it disappears fast. There is no single coverage number, only a coverage number per thickness, which is why every honest answer to this question is a small table rather than one figure.
The relationship is easy to verify with this site's engine. A 9 × 9 ft slab — 81 square feet — poured at 4 inches computes to exactly 27.00 cubic feet, which is exactly 1.00 cubic yard. Change either the footprint or the thickness and the yard count moves in direct proportion: double the thickness and one yard covers half the area.
The 324 rule, and coverage at common depths
The general formula falls out of the unit conversion. Coverage in square feet × (thickness in inches ÷ 12) must equal 27 cubic feet, so coverage = 27 × 12 ÷ thickness = 324 ÷ thickness-in-inches. At 3 inches one yard covers 108 square feet; at 4 inches, 81; at 5 inches, 64.8; at 6 inches, 54; at 8 inches, 40.5.
Each of those rows can be checked as a real slab in the calculator, and they all return exactly 1.00 cubic yard: a 12 × 9 ft slab at 3 inches, a 9 × 9 ft slab at 4 inches, an 8.1 × 8 ft slab at 5 inches, a 9 × 6 ft slab at 6 inches, and a 9 × 4.5 ft slab at 8 inches all compute to 27 cubic feet on the nose. The 324 rule is not an approximation — it is the same arithmetic the engine runs, rearranged.
Working backwards: how many yards a real slab takes
In practice the question usually arrives inverted: not "what does a yard cover" but "how many yards does my slab need". Divide the slab's cubic feet by 27. A 10 × 20 ft parking pad at 4 inches is 66.67 cubic feet, or 2.47 cubic yards formed. A 20 × 20 ft driveway at 5 inches is 166.67 cubic feet — 6.17 cubic yards. A 24 × 24 ft two-car garage slab at 6 inches is 288 cubic feet, a substantial 10.67 cubic yards.
Those are all engine outputs, and they show how quickly thickness compounds with footprint: the garage slab has only 1.4 times the area of the driveway but needs 1.7 times the concrete, because it carries an extra inch of depth across the whole footprint. When a budget needs trimming, depth and footprint are the only two levers — and code or load requirements usually fix the depth, which is why footprint is where most plans get adjusted.
Formed volume versus the volume you order
The coverage table describes geometry; an order has to survive a job site. Subgrade dips make the real slab thicker than nominal in spots, mix is lost in the chute and the wheelbarrow, and edges over-excavate — so the trade convention is to order 5–10% over the formed volume. With the calculator's default 10% waste factor, the 10 × 20 ft pad's 2.47 cubic yards becomes 2.72 to order, the 20 × 20 ft driveway's 6.17 becomes 6.79, and the garage slab's 10.67 becomes 11.73.
Ready-mix suppliers quote in fractional-yard increments and commonly charge a short-load fee on small deliveries, so get the quote on the waste-adjusted figure, not the formed one. Running short mid-pour creates a cold joint where a second batch meets half-set concrete — the one outcome that costs more than the extra fraction of a yard.
Sanity-checking a yard in bags
Bags give the coverage number a physical scale. Using the published QUIKRETE yields (about 0.60 cubic feet per 80-lb bag, checked 2026-06-10), one cubic yard equals 45 80-lb bags — roughly 3,600 pounds of dry mix. Per bag, that is about 1.8 square feet of slab at a 4-inch depth: an 80-lb bag barely covers a doormat.
That equivalence is the fastest way to pick a supply method. A pour measured in single bags — post holes, a stoop pad — is a store run. A pour measured in yards is a truck: the 6.79-yard driveway order would be more than 300 80-lb bags mixed by hand against a setting clock. When the coverage table says your project needs more than about one yard, price a ready-mix delivery before counting bags.
Questions
- How many square feet does a yard of concrete cover at 4 inches thick?
- 81 square feet — 27 cubic feet divided by a 4-inch (one-third foot) depth. A 9 × 9 ft slab at 4 inches is exactly one cubic yard.
- How many cubic feet are in a cubic yard of concrete?
- Exactly 27 — a cubic yard is a 3 × 3 × 3 ft cube. Divide a slab's cubic feet by 27 to get the cubic yards a ready-mix supplier quotes.
- How many yards of concrete do I need for a 20 × 20 driveway?
- At 5 inches thick, 6.17 cubic yards formed — 6.79 cubic yards with the calculator's default 10% waste factor, which is the figure to order.
- Does the coverage table already include a waste factor?
- No. The 324 ÷ thickness rule is pure geometry. Add 5–10% before ordering; the calculator applies a 10% default and shows both figures.