A full-sized acoustic guitar is 40 to 42 inches in length. A full-sized guitar is also referred to as a "4/4," with the smaller sizes being three-quarter, one-half and one-quarter.
The smaller-sized guitars came about as a way of helping children learn how to play the instrument. By using a smaller scale, the frets are closer, allowing smaller hands to play the chords without much difficulty. The size of a guitar also has a direct effect on the type of sound it produces. Smaller guitars are usually used to accentuate high-end trebles, while larger guitars are associated with bass frequencies.