Same arithmetic as mulch, different depths, and one extra layer nobody accounts for. A driveway is not one depth of gravel, it is two or three different materials stacked.
This is the number that changes everything, and unlike mulch there is no single right answer.
Going deeper than needed on decorative gravel is wasteful and makes the surface unpleasant to walk on, since deep loose stone shifts underfoot. Going shallower than needed on a drive means you will be topping it up every year.
Straight sided areas are length times width. Split awkward shapes into rectangles and triangles, and for a curved bed approximate with a rectangle at the average dimensions.
Driveways are usually the awkward one, because they are long, often taper, and frequently have a turning area at one end. Measure the width at several points along the run and average it, then treat the parking or turning area as a separate rectangle and add it.
A laser measure handles a long driveway run easily if there is a garage door or a wall at the far end to shoot. If it opens onto a road with nothing to aim at, prop a board at the end or use a wheel. This limitation is covered properly in the land guide.
Cubic yards equals length in feet times width in feet times depth in inches, divided by 324.
A path 40 feet long and 3 feet wide at 3 inches: 40 times 3 times 3 is 360, divided by 324 is 1.11 cubic yards.
By coverage, one cubic yard gives roughly 162 square feet at 2 inches, 108 at 3 inches, and 81 at 4 inches. Full conversions here.
Unlike mulch, weight is a real constraint here. A cubic yard of gravel typically runs well over a ton, and wet aggregate more still. Before ordering, check that your delivery access and any vehicle you plan to move it with can handle it, and ask the supplier for the weight rather than working from volume alone.
A gravel driveway that lasts is not a single depth of decorative stone. It is typically a coarse base course, sometimes a middle layer, and then the surface gravel you actually see.
That means calculating each layer separately at its own depth over the same area, then adding the volumes. A drive with a 4 inch base and a 3 inch surface needs the volume for both, and if you order only for the surface you will end up with stone sitting directly on soil, which sinks, rutted and full of weeds within a season.
Specific depths for base courses vary with soil conditions, drainage and expected traffic, so this is worth asking your aggregate supplier about for your site rather than applying a generic figure. What matters for measuring is that you calculate per layer rather than once.
Gravel compacts substantially, especially base layers that are mechanically rolled. The depth you order at is the loose depth, and it will settle noticeably below that.
This is why the standard 5 to 10 percent allowance is the floor rather than the ceiling for gravel, and why base courses in particular are usually ordered generously. Suppliers can advise on the compaction factor for the specific material, since it varies with stone size and angularity.
Uneven ground compounds it. Ruts and hollows swallow material without changing the finished level, and a drive that has been in use for years is rarely flat. Driveway measurement is covered in more detail here, and mulch follows the same formula with narrower depths.
For the wider picture on choosing a laser measure, including what the specifications actually mean, start on our front page.