Multiply the area you are covering by the depth in inches and divide by 324 — that is the order in cubic yards. A 10×10 ft area is 100 sq ft, so at 3 inches deep it takes 100 × 3 ÷ 324 = 0.93 cubic yards, which is 25 cubic feet, about 1.3 tons of typical gravel and 50 bags of 0.5 cu ft. The same 100 sq ft at 2 inches needs 0.62 cubic yards (34 bags, roughly 0.9 ton) and at 4 inches 1.23 cubic yards (67 bags, about 1.7 tons). One cubic yard covers 324 sq ft at 1 inch, 162 at 2 inches, 108 at 3 inches and 81 at 4 inches.
The formula, in three steps
- Get the area. Length × width in feet. An L-shaped bed or a dog-leg driveway is two rectangles added together.
- Turn the depth into feet. Divide the inches by 12 — 1 in = 0.083 ft, 2 in = 0.167 ft, 3 in = 0.25 ft, 4 in = 0.333 ft, 6 in = 0.5 ft.
- Do the volume math. Cubic feet = area × depth in feet. Divide by 27 for cubic yards, then by the bag size for a bag count, and round up.
| Unit you want | Formula |
|---|---|
| Cubic feet | sq ft × depth in inches ÷ 12 |
| Cubic yards (bulk) | sq ft × depth in inches ÷ 324 |
| Tons | cubic yards × density in tons per yard |
| 0.5 cu ft bags | cubic feet × 2, rounded up |
The 324 is 27 cubic feet per yard × 12 inches per foot, which is why a yard covers 324 sq ft at exactly 1 inch. Clemson’s Home & Garden Information Center works from the same two constants — 27 cubic feet in a cubic yard, a yard covering 324 sq ft an inch deep. The gravel calculator runs the formula and returns yards, tons and bags at once; the square footage calculator settles the area for circles and triangles.
How much one cubic yard covers
| Depth | One cubic yard covers | One 0.5 cu ft bag covers |
|---|---|---|
| 1 in | 324 sq ft | 6 sq ft |
| 2 in | 162 sq ft | 3 sq ft |
| 3 in | 108 sq ft | 2 sq ft |
| 4 in | 81 sq ft | 1.5 sq ft |
| 6 in | 54 sq ft | 1 sq ft |
Both columns are volume divided by depth: 27 ÷ 0.25 = 108 sq ft at 3 inches, and 0.5 ÷ 0.25 = 2 sq ft for a half-cubic-foot bag — the figure retail labels print. Read the cubic footage on the bag before buying; 0.5 cu ft is the common retail size and the count per yard depends entirely on it.
Cubic yards to tons
Weight is where the order gets tricky, because gravel is sold by volume at the quarry and by weight on the road. The density is the bridge:
| Material | Tons per cubic yard | Pounds per cubic yard |
|---|---|---|
| Gravel, ¼–2 in | 1.4–1.7 | 2,800–3,400 |
| Pea gravel | 1.25–1.5 | 2,500–3,000 |
| Rock, 2–6 in | 1.1–1.4 | 2,200–2,800 |
Inch Calculator’s chart gives those ranges and notes that most gravel weighs 1.4 to 1.7 tons per cubic yard. The 1.4 figure is the safe default for mixed crushed stone; pea gravel sits lower because rounded pieces trap more air. At 1.4:
- 1 ton = 0.71 cubic yards = 19.3 cubic feet, so a ton covers about 116 sq ft at 2 inches, 77 sq ft at 3 inches and 58 sq ft at 4 inches.
- At the heavy end, 1.7 tons per yard, a ton is only 0.59 cubic yards and 2 inches of cover drops to about 95 sq ft.
How deep should the gravel be
| Use | Depth | Source |
|---|---|---|
| Weed control under a decorative bed | 1 in of small rock | Clemson HGIC 1604 |
| Inorganic mulch: gravel, crushed stone, lava rock | 2–3 in | Utah State University Extension |
| Driveway surface course, finished | 6 in compacted | Penn State DSA bulletin |
| Driveway surface course, lighter traffic | 4.5 in compacted | Penn State DSA bulletin |
| Loose depth to place for a 6 in finish | 8 in | Penn State DSA bulletin |
| Crown or cross-slope on a driveway | ½–¾ in per foot | Penn State DSA bulletin |
The two landscape figures do different jobs: Clemson’s 1 inch is the minimum that stops weeds around permanent plantings, while Utah State’s 2 to 3 inches is the finish depth for inorganic mulch as a design surface. Below 1 inch, sunlight reaches the soil and the stone stops being mulch.
Driveways are a different problem. Penn State’s Center for Dirt and Gravel Road Studies spells out the compaction loss: its driving surface aggregate “can be placed at in an 8 inch depth and compacted to 6 inches, or in a 6 inch depth and compacted to 4½ inches.” The same bulletin warns that “the performance of any aggregate or pavement will be limited by the stability of the base it is placed on.”
Worked examples you can copy
| Area | 2 in deep | 3 in deep | 4 in deep | 6 in deep |
|---|---|---|---|---|
| 3 × 40 ft path (120 sq ft) | 0.74 | 1.11 | 1.48 | 2.22 |
| 10 × 10 ft bed (100 sq ft) | 0.62 | 0.93 | 1.23 | 1.85 |
| 10 × 20 ft bed (200 sq ft) | 1.23 | 1.85 | 2.47 | 3.70 |
| 20 × 20 ft pad (400 sq ft) | 2.47 | 3.70 | 4.94 | 7.41 |
| 12 × 50 ft driveway (600 sq ft) | 3.70 | 5.56 | 7.41 | 11.11 |
Cubic yards, rounded up. Multiply any cell by 1.4 for tons of mixed gravel or by 54 for bags of 0.5 cu ft. Two cases that do not fit the grid:
- Gravel mulch around shrubs. A 40 ft × 3 ft strip is 120 sq ft. At Utah State’s 2-inch depth that is 120 × 2 ÷ 324 = 0.74 cubic yards, about 1 ton, or 40 bags. Drop to the 1-inch weed-control layer and it halves: 0.37 cubic yards and 20 bags.
- New gravel driveway, 12 × 50 ft. Finished at 6 inches it measures 11.1 cubic yards, but you order the loose depth: 600 × 8 ÷ 324 = 14.8 cubic yards, about 20.7 tons. With the 10% overage that becomes 16.3 cubic yards, roughly 22.8 tons — and 880 bags, if you were foolish enough to buy it bagged.
Add 10% for waste, a third more for compaction
Two allowances stack, and they are not the same thing.
| Allowance | How much |
|---|---|
| Overage | +10% |
| Compaction | ×1.33 (8 in loose → 6 in finished) |
Inch Calculator recommends the 10% overage by default — it pays for spillage, wheelbarrow losses and low spots in the subgrade — and warns that compaction can cost up to 30% of the volume on road work, the same order as Penn State’s 8-to-6 ratio. A hand-raked path needs only the 10%; a plate-compacted driveway needs finished volume × 1.33 first, then +10%.
Bags vs bulk
| Quantity | Value |
|---|---|
| Bags per cubic yard, by bag size | 54 at 0.5 cu ft · 36 at 0.75 cu ft · 27 at 1 cu ft |
| One 0.5 cu ft bag covers | 3 sq ft at 2 in · 2 sq ft at 3 in |
Bagged stone costs more per cubic foot, so it works for a 100 sq ft bed at 2 inches (34 bags) and stops making sense for a driveway (880). Bulk is quoted in cubic yards; the crossover is about one cubic yard, since 54 bags is more than most people want to carry. If your supplier quotes cubic feet or cubic meters, the cubic yards calculator converts them.
Pea gravel or crushed stone
The shape of the stone decides where it belongs. Crushed stone has angular faces that lock together under a roller, and Penn State’s spec depends on it: its aggregate carries 11 to 15% fine material so the mix packs into a dense surface. Pea gravel is round, so it shifts underfoot — fine for beds and path edges, poor for anything a car drives on. It is also lighter, 1.25 to 1.5 tons per cubic yard, so 0.93 cubic yards for a 10×10 ft bed weighs 1.2 to 1.4 tons instead of 1.3. Replacing mulch in an existing bed? The mulch calculator already has the area and uses the same 324 divisor.
Quick checklist
- Measure each area in feet; split L-shapes into rectangles.
- Pick the depth: 1 in for weed control, 2 to 3 in for stone beds, 6 in compacted (8 in loose) for a driveway.
- Cubic yards = sq ft × depth in inches ÷ 324.
- Tons = cubic yards × density: 1.4 mixed gravel, 1.25–1.5 pea gravel, 1.1–1.4 large rock.
- Compacted work: finished volume × 1.33, then +10% for spillage.
- Bags = cubic feet ÷ the volume on the label; a yard is 54 bags of 0.5 cu ft.
- Keep the crown: ½ to ¾ inch of fall per foot.