Which stone
Pick the stone from the list on the calculator and the density and usual depth follow. The difference between them is not the price per ton so much as what each one does once it is down.
#57 crushed stone, ¾ in 1.4 tons/yd³ · usually 4 in
The all-purpose stone: angular, washed, no fines. It locks together well enough for a driveway surface and drains fast because there is nothing small to clog the gaps — which is why it is the stone for French drains, drainage beds and the layer under a slab that stops water wicking up. Sold as #57 in most of the country, ¾ inch clean or ¾ inch washed elsewhere.
Crusher run / road base, ¾ in minus 1.5 tons/yd³ · usually 4 in
Crushed stone with the fines left in, from ¾ inch down to dust. It compacts into a hard crust that does not drain, and that is the point: it is the base under pavers, a patio, a shed, a driveway — 4 inches for foot traffic, 6 or more for cars. Order it for anything that has to stay put, never for anything that has to drain. Also sold as dense-grade, ABC or 21A.
Limestone, #57 or screenings 1.45 tons/yd³ · usually 4 in
The same grades as crushed stone wherever the quarry is limestone — the Midwest, the South, much of the East. Lighter in colour, a little dustier, and slightly heavier per yard. Limestone screenings, the fine leftover, bed pavers in some regions. It raises soil pH over the years, so keep it away from beds of acid-loving plants.
Decomposed granite 1.5 tons/yd³ · usually 3 in
Granite weathered to gravel and grit, the path material of the West and Southwest. Laid 3 inches and compacted it makes a firm, natural-looking surface. For a stabilized mix, follow the binder manufacturer's mixing, watering and depth instructions. Sold by the ton or the yard; the colours run from gold to grey by quarry.
Pea gravel, ⅜ in 1.3 tons/yd³ · usually 3 in
Small rounded stone that rolls underfoot and never compacts. Right for beds, play areas, between stepping stones and as a top dressing; wrong as a base for anything. It migrates, so it needs an edge to stay where you put it. Goes down 2 to 3 inches.
For rounded decorative stone — river rock, cobbles, Mexican beach pebble — use the river rock calculator: the depth rules are different and it is often sold by the bag.