Cross reference a drive belt using a drive belt cross reference chart. Find the standard belt number or manufacturer's model number for your belt on the chart. Every belt on the same row as your belt is fully compatible with it.
If don't have access to either the standard belt number or a manufacturer's model number, you can still find compatible drive belts using the belt's length. Measure the belt's length along its outside wall, and find that length on the chart. For example, if you measure the old drive belt's outside length at 42 inches, that belt is compatible with Grainger's A40 belt, Goodyear's A40 (4L420) and Dayco's AP40 model. Most belts from generic manufacturers use the standard belt number, which is the same as Grainger's A40 designation for this belt. If a belt measures slightly over an individual inch, round the length down to the nearest even inch, as belts can stretch slightly after years of use.
Using a drive belt cross reference can save you considerable money. Drive belts from original equipment manufacturers are typically much more expensive than belts produced by dedicated parts manufacturers. Often, aftermarket belts are actually produced by parts manufacturers like Goodyear, Dunlop or Grainger, as original equipment manufacturers often contract with these companies instead of producing the belts themselves.