Crushed stone is ordered in tons. First compute cubic yards, then multiply by density. A widely used planning density for crushed stone is about 1.4 tons per cubic yard (roughly 2,800 lb/yd³). Denser rock can run 1.5–1.7 tons/yd³—use your quarry’s number if you have it.
Driveways often use 4 inches of compacted base. A 20×10 ft pad 4 inches deep is 2.47 cubic yards, or about 3.45 tons at 1.4 tons/yd³.
Order a little extra if the subgrade is uneven or you will compact in lifts.
Garden beds against the same pad use the soil calculator. If you only have length and width so far, get the area from the square foot calculator.
How this calculation works
cu yd = L × W × (depth/12) ÷ 27. tons = cu yd × density (default 1.4 t/yd³).