A grand concert guitar measures 19 3/8 inches long, 4 3/4 inches deep and 8 3/8 inches wide at the waist, according to CB Guitars. An auditorium-size guitar measures the same length, but is 4 1/8 inches deep and 9 3/16 inches wide at the waist.
Guitars range in length, width and depth, depending on their type. A guitar's size and shape determine its general sound, volume and tonal qualities. Dreadnought guitars measure 20 inches long, 4 7/8 inches deep and 10 3/4 inches wide at the waist. Electric guitars tend to be thinner and smaller than acoustics, because the string's sound can be amplified electronically.