The short answer: measure your area in square feet, multiply by depth in feet, divide by 27 for cubic yards, then multiply by the stone's density in tons per yard. For the classic example — a 20-by-10-foot driveway at 3 inches deep with crushed stone — that is 200 × 0.25 = 50 cubic feet, or 1.85 cubic yards, times 1.5 tons per yard = 2.78 tons. Order 3 tons. Every step matters: skipping one is how people end up paying for a second delivery.
Step one is area, and it has to be the real area, not the sketch. Measure length times width in feet after your edging is set, because edging defines the true boundary. For L-shaped areas or curved beds, split the space into rectangles and add them up, then shave 10 to 15% off for curves — a rectangle drawn around a curve overstates the area. The same splitting trick works for any odd shape: two rectangles beat one optimistic guess every time.
Step two is depth, and this is where the units trip people up. Depth on site is measured in inches, but the formula needs feet: divide inches by 12. Three inches is 0.25 feet, two inches is about 0.167 feet, four inches is 0.333 feet. Multiply area by depth in feet for cubic feet, then divide by 27 — there are 27 cubic feet in a cubic yard — for cubic yards. Our driveway: 200 square feet × 0.25 feet = 50 cubic feet, and 50 ÷ 27 = 1.85 cubic yards. Skip the inch-to-foot conversion and you will order twelve times too much stone.
Step three converts volume to weight, because suppliers sell by the ton. Multiply cubic yards by the material's bulk density: about 1.5 tons per cubic yard for crushed stone, 1.4 for pea gravel, 1.45 for river rock, and 1.3 for decomposed granite. These are quarry rules of thumb — actual density varies with stone size and moisture — so if your supplier publishes their own figure, use theirs. The coverage check runs the same math backward and is the fastest way to sanity-check a quote: one ton of crushed stone covers about 72 square feet at 3 inches, 108 at 2 inches, and 54 at 4 inches. If a supplier's quote implies wildly different coverage, ask questions before you pay.
Depth is a decision, not a guess, and it depends on what the gravel has to do. Walkways and decorative beds need only 2 inches — enough to cover the ground and suppress weeds. A driveway top layer wants 3 to 4 inches, and a proper new driveway is built in two layers: a 4-to-6-inch compacted base of crusher run or road base, topped with 2 to 3 inches of clean stone. Patio bases follow the same logic, with 4 to 6 inches of compacted base under pavers. Going thinner is false economy: soil shows through after the first hard rain, and topping up later costs a second delivery fee.
Material choice matters as much as quantity. Crushed stone has angular faces that lock together under weight, which is why it is the default for driveways and bases — it stays put. Pea gravel is small, smooth, and rounded, so it shifts underfoot and migrates toward low spots; it looks beautiful in beds and paths but makes a poor driveway surface. River rock is decorative and heavy, best for borders and dry creek beds rather than anything you walk or drive on. Decomposed granite compacts into a firm, natural-looking path surface, but it needs edging to contain it and periodic replenishment. Pick the material for the job first, then run the quantity math with that material's density.
Five ordering mistakes account for most gravel regrets. First, ordering exactly the calculated tonnage with no waste allowance: add 5 to 10% for driveways, curves, and slopes, where stone migrates downhill and spills past edges. Second, forgetting supplier minimums — most deliveries start at 1 ton, so a small walkway job that calculates to 0.83 tons (a 12-by-8-foot path at 2 inches in pea gravel) still means ordering a full ton. Third, confusing tons and yards: they are not interchangeable, and a supplier quoting yards while you budgeted tons will surprise you. Fourth, wet gravel: stone loaded after rain can weigh 10% more, and if you buy by the ton you are paying for that water — ask for the scale ticket. Fifth, measuring depth from the top of loose soil instead of from finished grade, which inflates or deflates the whole order.
A final ordering checklist before you call. Confirm the material and its density with your supplier, and confirm whether the price is per ton or per yard. Ask about the delivery fee and the minimum, and whether combining two projects into one load saves a fee — it usually does. Make sure the truck can reach the drop point; a long wheelbarrow haul from the street is the hidden labor cost of every gravel project. Leftover gravel is not waste: it stores indefinitely, and a half-ton pile by the shed is next year's top-up, already paid for. Run your exact numbers through the Gravel Calculator before you order, and the delivery that arrives will be the delivery you actually need.