To calculate cubic yards, measure your project in feet — length, width and depth — multiply the three together to get cubic feet, then divide by 27. That single division is the whole trick: a cubic yard is a cube 3 feet on each side, so it holds 3 × 3 × 3 = 27 cubic feet. A 10 × 10 ft concrete slab poured 4 inches thick is 33.3 cubic feet, which is 1.23 cubic yards. Everything else in this guide — circles, irregular beds, bag counts, waste allowances — is this same method dressed for different shapes and materials.
The conversions worth memorizing are few. 1 cubic yard = 27 cubic feet. 1 cubic yard = 46,656 cubic inches, which you will rarely need. 1 cubic yard ≈ 0.76 cubic meters, which you will need if a supplier or a plan is metric. Depth is where errors creep in, because depths are quoted in inches while lengths are in feet: 1 inch = 0.083 ft, 2 inches = 0.17 ft, 3 inches = 0.25 ft, 4 inches = 0.33 ft, 6 inches = 0.5 ft, 12 inches = 1 ft. Convert the depth to feet before you multiply, every time. If you prefer to check your arithmetic, the cubic yard calculator accepts feet, inches or meters and shows the same steps.
Measuring so the volume is real
Measure with the material's behavior in mind. Depths are rarely as even as the plan: a slab base dug by eye varies by half an inch, and half an inch over 100 sq ft is about 4 cubic feet — roughly 0.15 cubic yards you did not order. Pros run string lines or a laser across the excavation and probe the depth in a grid, then average; for soil and mulch beds, measuring in three or four spots and averaging is plenty. Lengths and widths should be measured at the surface the material will actually cover, including any flare at the edges of a dug bed, because volume follows the real hole, not the tidy drawing.
Method 1: rectangles and slabs
For rectangles and slabs — the most common case — the formula is length × width × depth, all in feet, divided by 27. Worked example: a 10 × 10 ft slab at 4 inches. Depth: 4 ÷ 12 = 0.33 ft. Volume: 10 × 10 × 0.33 = 33.3 cubic feet. Yards: 33.3 ÷ 27 = 1.23 cubic yards. Concrete is ordered with a waste and spillage allowance of about 5-10 percent, and trucks sell in quarter- or half-yard steps, so this slab is realistically a 1.5-yard order. The pattern generalizes: patios, shed bases, footings and garden beds are all rectangles once you square off the edges, and slightly over-measuring a rectangle is always safer than under-ordering.
Method 2: circles
For circles, replace length × width with π × radius², then multiply by depth and divide by 27. Worked example: a circular planting bed with a 6 ft radius, filled 3 inches deep. Area: 3.1416 × 6² = 3.1416 × 36 = 113.1 sq ft. Volume: 113.1 × 0.25 = 28.3 cubic feet. Yards: 28.3 ÷ 27 = 1.05 cubic yards. The same method sizes round hot-tub pads, fire-pit surrounds and tree rings. Two habits prevent most circle errors: use the radius (center to edge), not the diameter, and square the radius before multiplying by π — squaring the diameter by mistake quadruples your order.
Method 3: irregular areas
Irregular areas yield to two approaches. The split method divides the shape into rectangles, calculates each, and adds them: an L-shaped bed made of an 8 × 10 ft rectangle plus a 6 × 4 ft rectangle at 4 inches deep is (80 + 24) × 0.33 = 34.3 cubic feet, or 1.27 cubic yards. The averaging method suits gently irregular beds: measure the length at a few points and average them, do the same for width, then treat it as a rectangle — a bed measuring 18, 20 and 22 ft along its length averages 20 ft, and at 5 ft wide and 6 inches deep that is 20 × 5 × 0.5 = 50 cubic feet = 1.85 cubic yards. Splitting is more accurate; averaging is faster and fine for loose materials like mulch.
When the material comes in bags
Bagged material is sold by the cubic foot, which reverses the usual shopping math. One cubic yard is 27 cubic feet, so it equals thirteen and a half of the common 2-cubic-foot mulch bags, or fifty-four 0.5-cubic-foot bags of gravel or soil. To find a bag count for a real job, work in cubic feet and skip yards entirely: the 1.23-cubic-yard slab above is 33.3 cubic feet, and if it were a mulch bed instead of concrete it would need 33.3 ÷ 2 = 16.7, so 17 bags of 2-cubic-foot mulch. The cut-off is practical rather than mathematical: somewhere around 2 to 3 cubic yards, bulk delivery almost always beats bags on price and effort, as the bag counts pass into the hundreds of pounds of hauling.
Notes for concrete, soil, mulch and gravel
Each material bends the basic number slightly. Concrete wants a 5-10 percent waste allowance for spillage, uneven subgrade and pump or wheelbarrow residue, and a slab that measures 4 inches rarely averages 4 inches once the base settles. Soil and compost compact after watering and settling, so a bed filled to the brim today may sit an inch lower in a month; ordering a little extra is standard. Mulch fluffs when spread and then settles, which is why coverage claims on bags assume a fresh 3-inch layer. Gravel is sold by the ton as often as by the yard, and converting needs its density — about 1.4 tons per cubic yard — which the gravel calculator applies for you; our companion guide on how much gravel you need covers depths and delivery in detail.
Ordering has its own vocabulary. Concrete trucks carry up to about 10 cubic yards per load and most plants add a short-load fee for small orders, so a 1.5-yard slab can cost nearly as much delivered as 4 yards does — batch small concrete jobs together when you can. Bulk soil, mulch and gravel yards load by the bucket, commonly in half-yard or whole-yard steps, and delivery is usually a flat fee within a radius, which rewards ordering the full amount once. Bagged material avoids delivery fees entirely but trades them for trips and lifting. Ask two questions before paying: what is the minimum load, and what does a return trip cost? The answers decide whether rounding up generously is smart or wasteful for your project.
A complete example, start to finish
Here is a complete job run start to finish: raised-bed soil for a 20 × 4 ft vegetable bed, filled 6 inches deep after settling, with an extra allowance for compaction. Depth in feet: 6 ÷ 12 = 0.5 ft. Volume: 20 × 4 × 0.5 = 40 cubic feet. Yards: 40 ÷ 27 = 1.48 cubic yards. Compaction allowance at 10 percent: 1.48 × 1.1 = 1.63 yards. Order decision: bulk yards usually come in whole or half steps, so order 1.5 yards if the supplier allows a top-up, or 2 yards if delivery fees make a second trip expensive. If bagging instead: 40 × 1.1 = 44 cubic feet ÷ 2-cubic-foot bags = 22 bags. Every cubic-yard job on earth reduces to this same sequence of five decisions.
Cylinders and post holes
Cylindrical holes use the circle method in miniature. A fence post hole 1 ft across (radius 0.5 ft) and 3 ft deep holds π × 0.5² × 3 = 3.1416 × 0.25 × 3 = 2.36 cubic feet, which is 2.36 ÷ 27 = 0.087 cubic yards. Twenty such holes for a fence line take 20 × 0.087 = 1.75 cubic yards of concrete or gravel — a figure that surprises people who pictured a few bags. Bagged concrete is sold by weight and yield (a common 80 lb bag yields about 0.6 cubic feet), so holes are one case where the bag math runs first: 2.36 ÷ 0.6 = about 4 bags per hole before waste, less whatever volume the post itself displaces.
Coverage quick reference
A few coverage figures are worth keeping on your phone because they shortcut the whole calculation for flat work at standard depths. At 2 inches deep, 1 cubic yard covers 162 sq ft; at 3 inches, 108 sq ft; at 4 inches, 81 sq ft; at 6 inches, 54 sq ft; at 12 inches, 27 sq ft. The pattern is simple: coverage is 324 ÷ depth in inches. So a 500 sq ft lawn to be top-dressed at 3 inches needs 500 ÷ 108 = 4.6, call it 5 cubic yards of compost. These figures assume a perfectly flat spread, so treat them as the floor of the order, not the ceiling, and let the waste allowances above do their work.
Common cubic yard mistakes
The recurring mistakes are easy to spot once you have seen them. Leaving depth in inches inside the multiplication — the single most common error — overstates the order by a factor of 12. Dividing by 9 instead of 27 confuses square yards with cubic yards and understates by a factor of 3. Rounding down to the cheaper load, then paying a short-load or second-delivery fee that wipes out the saving. Forgetting waste on concrete, where being half a yard short mid-pour is the worst version of the problem. And mixing units mid-quote, comparing one supplier's tons against another's yards with no density conversion. Run each figure through the divide-by-27 step slowly and most of these disappear.
However you measure, the safe routine is: convert everything to feet, multiply, divide by 27, add the material's allowance, then round up to what the supplier actually sells. If you want a second opinion on the arithmetic before you order, enter the same dimensions into the cubic yard calculator and compare results — agreement between hand math and the tool is the cheapest quality check in the whole project. Cubic yards look intimidating only because suppliers quote them casually; underneath, it is one multiplication and one division, and now you have both.