Quick answer
To calculate how much gravel you need, multiply the area (length × width in feet) by the depth in feet, then divide by 27 for cubic yards. A 20 × 10 driveway at 4 inches deep needs 2.47 cubic yards (about 3.46 US tons of pea gravel). Add 10–15% for compaction. Multiply by the gravel density (typically 1.25–1.5 tons per cubic yard) for weight.
The gravel calculation formula
The formula for calculating gravel volume is:
Cubic yards = (Length × Width × Depth in feet) ÷ 27
Convert depth from inches to feet by dividing by 12. A 4-inch gravel layer is 0.333 feet. The shortcut formula combines both steps:
Cubic yards = Square feet × Depth (inches) ÷ 324
To convert to tons, multiply cubic yards by the gravel's density:
US tons = Cubic yards × Density (tons per cubic yard)
Step-by-step: How much gravel do I need?
- Measure the length and width of your project area in feet.
- Decide on the gravel depth (typically 2–6 inches depending on project).
- Calculate cubic yards: length × width × (depth ÷ 12) ÷ 27.
- Add 10–15% for compaction and waste.
- Multiply by the gravel density (1.25–1.5 tons/cu yd) for weight.
- Multiply by price per ton for cost estimate.
Worked example: 20 × 10 foot driveway, 4 inches deep, pea gravel (1.4 tons/cu yd):
- Volume: 20 × 10 × (4 ÷ 12) = 66.67 cu ft = 2.47 cu yd
- With 10% waste: 2.47 × 1.10 = 2.72 cu yd to order
- Weight: 2.47 × 1.4 = 3.46 US tons (3.81 tons with waste)
- Cost at $50/ton: 3.81 × $50 ≈ $190 (material only)
How deep should gravel be for a driveway?
Gravel driveway depth depends on the layer and traffic:
| Layer | Typical depth | Notes |
|---|---|---|
| Driveway base | 4–6 in (compacted) | Order 25–30% extra loose |
| Driveway surface | 1–2 in | Top layer over compacted base |
| Garden path | 2–3 in | Over landscape fabric |
| Paver base | 4–6 in | Compacted, plus 1 in sand |
| French drain | 8–12 in | Washed #57 stone preferred |
| Landscaping bed | 2–3 in | Over weed barrier fabric |
Because loose gravel compacts about 20%, order 25–30% more than the compacted target volume for the base layer. A 20 × 10 driveway base at 6 inches compacted = 3.7 cubic yards compacted, so order about 4.6–4.8 cubic yards loose.
Gravel density and weight by type
Gravel density varies by stone type, gradation, moisture, and compaction. Use these typical values for planning, but confirm the exact density with your supplier.
| Material | US tons/cu yd | Common uses |
|---|---|---|
| Pea gravel | 1.40 | Paths, play areas, drainage |
| Crushed stone (¼–1 in) | 1.35 | Driveway base, paver base |
| Crushed stone (1–2 in) | 1.25 | Drainage, French drains |
| #57 washed gravel | 1.35 | Driveways, concrete aggregate |
| River rock | 1.25 | Landscaping, dry creek beds |
| Bank run gravel | 1.50 | Base fill, roadways |
| Decomposed granite | 1.30 | Paths, patios, xeriscaping |
| Limestone (crushed) | 1.30 | Driveways, base material |
How much area does gravel cover?
Coverage depends on depth. One cubic yard covers:
| Depth | Sq ft per cubic yard | Sq ft per US ton* |
|---|---|---|
| 1 inch | 324 | 231 |
| 2 inches | 162 | 116 |
| 3 inches | 108 | 77 |
| 4 inches | 81 | 58 |
| 6 inches | 54 | 39 |
*Per-ton coverage assumes 1.4 tons/cu yd (typical pea gravel).
How to calculate gravel for a driveway
A gravel driveway is built in layers: a 4–6 inch compacted base of crushed stone, topped with a 1–2 inch surface layer. Calculate each layer separately.
Standard 2-car driveway example (20 × 20 feet = 400 sq ft):
- Base at 6 inches: 400 × 6 ÷ 324 = 7.41 cu yd (order ~9.3 cu yd loose with 25% compaction)
- Surface at 2 inches: 400 × 2 ÷ 324 = 2.47 cu yd
- Total: ~11.8 cubic yards of gravel
At 1.4 tons/cu yd and $50/ton, material cost is about 16.5 tons × $50 = $825, plus delivery.
Gravel cost calculator
To estimate gravel cost, multiply the quantity by the unit price:
| Option | Typical price | Per cubic yard equivalent |
|---|---|---|
| Bulk (by ton) | $15–$75/ton | $21–$105/cu yd (at 1.4 t/cu yd) |
| Bulk (by cubic yard) | $20–$50/cu yd | $20–$50/cu yd |
| Bagged (0.5 cu ft) | $4–$8/bag | $216–$432/cu yd |
| Delivery fee | $30–$100 flat | — |
Example: A driveway needing 3.81 tons at $50/ton = $190.50 material + $60 delivery = $250.50 total. The same project bagged (about 206 bags at $5 each) would cost over $1,000.
Calculating gravel for circular areas
For round fire pits, circular patios, and round garden beds, use the cylinder formula:
Cubic yards = (π × radius² × depth in feet) ÷ 27
Example: A 10-foot-diameter fire pit (5 ft radius) at 4 inches deep: π × 5² × 0.333 = 26.18 cu ft ÷ 27 = 0.97 cubic yards. At 1.4 tons/cu yd, that is about 1.36 tons.
Accounting for compaction
Loose gravel delivered by truck takes up more volume than the same gravel after it is placed and compacted. A typical compaction factor is 20–25% — meaning 5 cubic yards of loose gravel becomes about 4 cubic yards after compaction.
If your project specifies a compacted depth (for example, a 4-inch compacted driveway base), order 25% more loose material to end up with the target compacted volume.
Pea gravel vs. #57 gravel: which to use
Pea gravel is small, rounded stone (¼–⅜ inch) used for paths, play areas, and decorative beds. It’s smooth but shifts underfoot — not ideal for driveways without edging. Density: about 1.4 tons per cubic yard.
#57 gravel is crushed stone (¾–1 inch) with angular edges that locks together when compacted. It’s the standard for driveway bases, concrete aggregate, French drains, and paver bases. Density: about 1.35 tons per cubic yard.
Use #57 for structural bases (driveways, slabs, pavers) and pea gravel for decorative surfaces (paths, beds, play areas). Many projects use both: #57 as the base, pea gravel as the surface.
How much gravel for a French drain
A French drain uses washed #57 gravel (no fines) to allow water flow. Calculate the trench volume minus the pipe volume:
Gravel = (trench length × width × depth) − (pipe volume) ÷ 27
For a 50-foot trench at 12 inches wide and 18 inches deep with a 4-inch pipe: trench = 50 × 1 × 1.5 = 75 cubic feet; pipe = 50 × 0.333 × 0.333 = 5.5 cubic feet; gravel = 69.5 cubic feet ÷ 27 = 2.57 cubic yards. Use washed #57 stone — crushed stone with fines will clog the drain.
How much gravel under a concrete slab
A gravel base under a concrete slab is 4–6 inches of crushed stone (#57 or similar). It provides drainage, prevents settling, and distributes load. For a 10 × 10 slab at 4 inches: 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.23 cubic yards. Add 10% for compaction, so order about 1.4 cubic yards.
For a 24 × 24 garage slab at 6 inches of gravel: 24 × 24 × 0.5 = 288 cubic feet ÷ 27 = 10.67 cubic yards. Order about 12 cubic yards with compaction. Compact the gravel in 2-inch layers before pouring.
How much gravel for pavers
A paver base needs 4–6 inches of compacted #57 gravel plus 1 inch of sand. For a 12 × 12 patio at 6 inches of gravel: 12 × 12 × 0.5 = 72 cubic feet ÷ 27 = 2.67 cubic yards. Add 25% for compaction, so order about 3.3 cubic yards of gravel plus 0.44 cubic yards of sand.
Frequently asked questions
Related calculators
For the volume math behind gravel, use the cubic yard calculator. For driveway paving, see the asphalt calculator. For instant results, use our free gravel calculator.