The standard widths for fabric bolts include 36, 38, 42, 44/45, 48, 54, 58, 59, 60, 72 and 108 inches, with 45, 54 and 60 inches being the most common. The width is often listed on a label at the end of a flat fabric bolt.
The amount of fabric needed for a project often depends upon the width of the material, which is often specified in commercial patterns. In general, the wider the fabric is, the less of it that is needed. Be certain of the amount of fabric required before it is cut by a store clerk, because some patterns require one long piece rather than multiple shorter pieces.