One ton is 0.51 to 4 cubic yards depending on the material: about 0.78 cubic yards of gravel, 0.99 cubic yards of dirt and 4 cubic yards of mulch. A ton here is a short ton of 2,000 lb, and each value is the published weight of a cubic yard of the material in the condition its document names: loose, compacted or not stated.
Weight per cubic foot and cubic yard with its condition in the document, tons per cubic yard, cubic yards per ton and the area one ton covers at 2 and 3 inches deep, by material, heaviest first; weights in different conditions are not comparable
To turn tons into cubic yards, multiply the tons by the cubic yards per ton. To turn cubic yards into tons, multiply by the tons per cubic yard. The area columns show how far one ton spreads at 2 and 3 inches deep; base and paving layers are usually thicker (see each material's published depths). For another depth, multiply the cubic yards per ton by 324 (the square feet one cubic yard covers at 1 inch) and divide by the depth in inches. A compacted weight gives compacted cubic yards: loose material for that layer takes more room.
The weight of the same material differs between suppliers, with moisture and with compaction, which is why the published values span a range. Each material's weight page lists every published value with its source; before ordering, ask the supplier for the weight per cubic yard of their material.