Medium 15"-16". Long 16" and Over. For 14" Viola D try a Prelude 4/4 Violin D String For 13" Viola D try a Prelude 3/4 Violin D String For 12" Viola D try a Prelude 1/2 Violin D String
D'Addario describes the Prelude strings as follows: Prelude strings are the educator’s preferred choice for student strings due to their unique blend of warm tone, durability, and value. Prelude strings have the warmest sound available in an affordable, solid steel core string design. Unaffected by temperature and humidity changes, they have excellent bow response.