A typical driveway uses a 4-inch compacted layer; enter length and width to get the volume and delivery tonnage.
A driveway wants a 4-inch compacted layer of angular stone, not decorative rounded gravel, and this view defaults to that depth. Build it in lifts with a plate compactor and set edging first, or it wanders into the lawn.
Why order extra? The headline number is the exact material your project needs. When you actually order, add about 5–10% on top — the “with 5% waste” figure in the result is a safe starting point. That margin covers what you lose to compaction, cuts around edges and corners, and ordinary spillage during handling. It is cheaper to have a little left over than to stop mid-job and wait on a second delivery.