How gravel is calculated
Gravel is ordered by volume, so the calculator turns your area and depth into cubic yards, adds an allowance for the stone that packs down when you compact it, and then converts the yards to tons using a typical weight for the stone you picked.
area (ft²) = length × width or π × (diameter ÷ 2)²
volume (ft³) = area × depth in inches ÷ 12
cubic yards = volume ÷ 27
yards to order = cubic yards × (1 + compaction % ÷ 100)
tons = yards to order × pounds per yard ÷ 2,000
bags = yards to order × 27 ÷ bag size in ft³, rounded up
Weights come from the material weight per cubic yard chart. They are for loose, moist stone as delivered; a load fresh out of the wash plant or straight after rain will weigh more.
Worked example: 20 × 10 ft patio base
The calculator opens on a 20 × 10 ft patio base, 4 in of crushed gravel with a 15% compaction allowance.
- Area: 20 × 10 = 200 ft².
- Volume: 200 × 4 ÷ 12 = 66.7 ft³.
- Cubic yards: 66.7 ÷ 27 = 2.47 yd³.
- With compaction: 2.47 × 1.15 = 2.84 yd³. Suppliers load by the half or whole yard, so order 3 yd³.
- Weight: 2.84 × 2,800 ÷ 2,000 = 3.98 tons.
How deep to lay gravel
Depth drives the order more than anything else: going from 4 in to 6 in adds half again as much stone. Typical depths are 2–3 in for the top course of a path, 4 in for a patio or shed pad base and 6–8 in for a driveway. Lay a driveway in compacted lifts rather than dumping the full depth and rolling once, and measure depth after compaction.
| Depth | ft² per yd³ | yd³ per 100 ft² | Typical use |
|---|---|---|---|
| 2 in | 162 | 0.62 | Path or walkway top course |
| 3 in | 108 | 0.93 | Path or walkway top course |
| 4 in | 81 | 1.23 | Patio or shed pad base |
| 6 in | 54 | 1.85 | Driveway, laid in compacted lifts |
| 8 in | 41 | 2.47 | Driveway, laid in compacted lifts |
Choosing the stone
Angular, crushed stone locks together when it is compacted, which makes it the right choice for driveways and bases. That locking is also why it needs a compaction allowance: the calculator flags any crushed stone set below 10%. Rounded pea gravel and river rock roll underfoot and stay loose, so they suit paths, drainage and decorative beds, and they need little extra.
| Material | lb per yd³ | tons per yd³ | yd³ per ton |
|---|---|---|---|
| Gravel / crushed stone | 2,800 | 1.40 | 0.71 |
| Pea gravel | 2,800 | 1.40 | 0.71 |
| Sand (general) | 2,700 | 1.35 | 0.74 |
| Crusher run / road base | 2,900 | 1.45 | 0.69 |
| Crushed limestone | 2,700 | 1.35 | 0.74 |
| River rock | 2,700 | 1.35 | 0.74 |
| Decomposed granite | 2,600 | 1.30 | 0.77 |
Quarries often sell by the ton rather than the yard. Use the weight line from the calculator for a ton price, and the yards line when it sells by volume.
Ordering and delivery
- Measure the area at ground level and split odd shapes into rectangles and circles. Enter each piece with “+ Add another area”; each can have its own depth, and the yards are added up before the order is rounded.
- Round the order up to the next half yard. Running short means a second delivery fee; a little extra stone is easy to use on a path or a low spot.
- Over about 10 yards is usually more than one truck. Ask the supplier what a full load is and whether a split load costs more.
- Bagged stone is for small repairs. At 54 bags to the yard, bulk is cheaper well before you reach a full yard.
- Pick a dump spot the truck can reach on firm ground, away from septic lids, and lay a tarp if the stone lands on a lawn.
Sources
- Geometry: rectangle area = length × width; circle area = π × (diameter ÷ 2)²; 1 yd³ = 27 ft³
- Material weight per cubic yard chart (typical loose, moist bulk densities from supplier data)
- Compaction allowance for crushed gravel base: 15–20% (common supplier and installer guidance)
- Bag size: 0.5 ft³ (50 lb) retail bag of gravel or stone