Gravel is a volume problem with a weight problem attached. The volume is simple geometry. The weight depends on the stone, and that is what the supplier may bill you for.
Volume (cu ft) = length (ft) × width (ft) × depth (ft)
Depth in feet = depth in inches ÷ 12
Volume (cu yd) = cu ft ÷ 27
Order = volume × (1 + allowance)
A 40 × 12 ft driveway at the depth you choose
The depth is yours to choose, and it should come from your project and your supplier’s advice rather than from this page. The three depths below are examples to show the effect on the quantity.
| Depth (example) | Volume to order | Estimated weight |
|---|---|---|
| 3 in | 4.89 yd³ | 7.34 tons |
| 4 in | 6.52 yd³ | 9.78 tons |
| 6 in | 9.78 yd³ | 14.67 tons |
This example assumes
- A 480 sq ft area (40 × 12 ft)
- 10% extra allowance, an editable planning default
- 1.5 tons per cubic yard, a rough planning value for weight and nothing more
The weight column is the least certain figure on the page. The planner labels it an estimate for exactly that reason, and the tons versus cubic yards guide covers why.
Calculated and ordered
At 4 inches the planner’s calculated volume, with the allowance, is 176 cu ft, and it shows 6.52 yd³ to order. Bulk gravel is not counted in bags, so the order is that volume rounded up to a hundredth of a cubic yard. If you buy bagged gravel, enter the bag volume and the planner counts bags.
What changes the estimate?
- The depth you choose for the job
- The allowance for compaction and uneven ground
- The density of your specific stone, which converts yards to tons
- The area: a driveway that widens or curves needs its area worked out first
What this does not decide
How much gravel a driveway needs structurally, and whether it needs a base under it, depends on the soil and the traffic. This guide converts a depth you have already chosen into a quantity.