Reference length: 34 inches: 86.63cm, 38 inches: 96.52cm, 40 inches:10/.6cm, 4 1 inch: 104. 14cm. The normal folk guitar is 40 or 4 1 inch, and the common guitars on the market are 4 1 and 40. Generally, there are D barrels, GA barrels and OM barrels.