Drive belt lengths vary greatly according to the power needed to be transmitted and the speeds of the driving and driven units. The width of drive belts are set according to the industrial standard part number by which they are coded. The most common industrial standard part numbers are A-section, B-section, C-section, D-section, E-section, AX-section and BX-section. A-section belts are 1/2-inch wide and D-section belts are 1 1/4-inches wide. All the other belt types have widths between these two extremes.
In addition to determining the width of drive belts, the industrial standard part number also helps in calculating the outer length of a given drive belt. A-section drive belts have outer lengths that are equal to their inner lengths plus 2 inches. B-section belts have an addition factor of 3 inches, while C-, D- and E-section belts have addition factors of 4 inches, 5 inches and 6 inches respectively. AX- and BX-section belts have addition factors of 2 inches and 3 inches respectively.
Drive belts are commonly coded with an industrial standard part number followed by the inner length of the belt in inches. Hence, a drive belt with a code A55 has a width of 1/2 inch and an outer length that is equal to (55+2) inches.