Here is the entire formula: multiply length by width by depth with every measurement in feet, then divide by 27. The answer is cubic yards. There is no second step and no trick — the only reason people get it wrong is that depth is almost always given in inches while length and width are in feet, and mixing those two units is what produces an order that is twelve times too big.
The 27 comes from geometry. A cubic yard is a cube 3 feet on every side, and 3 × 3 × 3 = 27. So a cubic yard is 27 cubic feet, always. Once you have the volume in cubic feet, dividing by 27 is the only conversion you need.
The one shortcut worth memorising is the coverage rule that falls out of it: one cubic yard spread 1 inch deep covers 324 square feet. Divide 324 by your depth in inches and you get the square footage a single yard will cover at that depth. At 3 inches, one yard covers 108 square feet. At 4 inches, 81. At 6 inches, 54.
Buying tip: Order about 5 to 10 percent over your calculated volume. Stone settles into the subgrade, spreads unevenly at edges, and dense-graded material loses roughly a quarter of its loose height once compacted. Running short means a second delivery fee of $50 to $150 for a fraction of a load.
Turn Inches Into Feet First
Every unit in the formula has to be feet before you multiply. Depth in inches divided by 12 gives depth in feet. That is the step people skip, and skipping it inflates the answer by a factor of twelve — the difference between ordering 7 yards and ordering 89.
| Depth in inches | Depth in feet | Sq ft per yd³ |
|---|---|---|
| 1 in | 0.083 | 324 |
| 2 in | 0.167 | 162 |
| 3 in | 0.25 | 108 |
| 4 in | 0.333 | 81 |
| 6 in | 0.5 | 54 |
| 8 in | 0.667 | 40.5 |
| 12 in | 1.0 | 27 |
Notice the last row: at a foot deep, a cubic yard covers 27 square feet, which is the same 27 showing up again. If your arithmetic ever disagrees with that table, the units are wrong somewhere.
Worked Examples
- Measure the area in feet. Length and width, at the widest points. Round up to the nearest half foot; nobody has ever regretted a slightly generous measurement.
- Convert the depth to feet. Inches divided by 12. Write it down rather than holding it in your head.
- Multiply all three. Length × width × depth = cubic feet.
- Divide by 27. That is your cubic yards.
- Add 5 to 10 percent. Waste, settling and compaction allowance.
A driveway base. 12 ft wide by 50 ft long, 4 inches of crusher run. Depth in feet is 4 ÷ 12 = 0.333. Volume is 12 × 50 × 0.333 = 200 cubic feet. Divide by 27 and you get 7.4 cubic yards. Add 10 percent for compaction and call it 8.2 yards. The same answer comes out of the coverage rule: 600 square feet ÷ 81 = 7.4. Cross-check either version against the gravel driveway calculator.
A garden path. 3 ft wide by 40 ft long, 3 inches of pea gravel. 3 × 40 × 0.25 = 30 cubic feet, or 1.1 cubic yards. Small jobs like this are usually cheaper by the bag-free scoop at the yard than by delivery, and you can size them fast with the pea gravel calculator.
A decorative bed. 200 square feet at 2 inches of river rock. Area is already known, so use coverage: 200 ÷ 162 = 1.2 cubic yards. At 1.5 tons per yard that is about 1.9 tons of river rock.
Irregular and Awkward Shapes
Almost no real yard is a clean rectangle, and you do not need it to be. Break the space into rectangles, triangles and circles, calculate the area of each, add them together, then apply depth once at the end. Depth is the same everywhere, so you only convert to volume once.
- Rectangle: length × width.
- Triangle: base × height ÷ 2. Useful for the wedge where a driveway flares into the road.
- Circle: radius × radius × 3.14. A 10 ft wide fire pit surround has a 5 ft radius, so 5 × 5 × 3.14 = 78.5 sq ft.
- Ring or border: outer circle area minus inner circle area.
- Curved bed: pace the outline, then approximate it as a rectangle using the average width. The error is smaller than your waste allowance.
For a trench — a French drain, a footing, a utility run — the shape is a rectangle stood on edge. Width in feet times depth in feet times length in feet, divided by 27. A 12-inch-wide, 24-inch-deep, 60 ft trench is 1 × 2 × 60 = 120 cubic feet, or 4.4 cubic yards of washed stone, less whatever the pipe displaces. The French drain calculator handles the pipe deduction for you. For step-by-step yard measuring technique, see how to measure your yard for stone.
Cubic Yards to Tons
Landscape yards sell by volume; quarries and trucking companies sell by weight. You will need both numbers on the phone. The conversion is simply cubic yards multiplied by the material’s density in tons per cubic yard.
| Material | Tons per yd³ | 10 yd³ weighs |
|---|---|---|
| Crusher run | 1.55 | 15.5 tons |
| Crushed stone | 1.5 | 15 tons |
| River rock | 1.5 | 15 tons |
| Sand | 1.5 | 15 tons |
| Gravel | 1.4 | 14 tons |
| Decomposed granite | 1.4 | 14 tons |
| Pea gravel | 1.35 | 13.5 tons |
| Topsoil | 1.1 | 11 tons |
A US ton is 2,000 pounds, and a tandem dump truck carries 13 to 15 tons — roughly 9 to 10 cubic yards of crushed stone. That matters for planning: if your job lands at 11 yards, you are paying for two trips, and it is often worth trimming a decorative layer by half an inch to stay inside one load. Run either direction with the tons to cubic yards calculator or the cubic yard calculator.
The Five Errors That Blow Up the Number
Every miscalculation we see traces back to one of a handful of causes, and all of them are catchable in thirty seconds if you know to look.
- Depth left in inches. The classic. Multiplying 12 × 50 × 4 gives 2,400 cubic feet and an answer of 89 yards instead of 7.4. If your result looks like a swimming pool, this is why.
- Dividing by 9 instead of 27. Nine converts square feet to square yards. Volume needs the cube.
- Confusing yards and tons. A supplier quoting “$40 a yard” and one quoting “$40 a ton” are not close to the same price — a yard of crushed stone weighs about 1.5 tons.
- Forgetting compaction. Dense-graded material such as crusher run loses roughly a quarter of its loose height once compacted. Order for finished depth, spread deeper.
- Calculating one layer for a two-layer job. A driveway is 4 inches of base plus 2 inches of surface, and they are different materials at different prices. Work them out separately, then add the tonnages.
One more habit worth building: write down the three numbers you multiplied, not just the answer. When the yard asks how you arrived at 8 yards, being able to say “600 square feet at 4 inches” lets them sanity-check you in one breath, and counter staff catch these errors for a living.
Bottom Line
Feet, feet, feet, divide by 27. Convert depth from inches before you multiply anything, break odd shapes into simple ones, add 5 to 10 percent for waste and settling, then multiply by density if the supplier quotes tons. Two sanity checks catch nearly every error: one yard covers 324 square feet at 1 inch, and one yard of stone weighs about a ton and a half. If your number fails either test, the units slipped somewhere — and it is worth catching before the truck is on its way. Depth choices are covered in how deep gravel should be.