Cello bows come in four different sizes, each corresponding to different cello sizes. The length of the bow is roughly analogous to the length of the back of the cello (when measured from the bottom of the cello up to the base of the button). While there are only four cello bow sizes, there are six cello sizes -- two of the bow sizes can be played for various cello sizes.
A full-size cello bow is 27 to 28 inches long -- the exact length can vary. A full-size bow corresponds to a full-size cello, which has a standard back length of 30 inches. Additionally, 7/8-sized cellos (back length of 29 inches) also use a full-size bow. This is the standard bow size for professional cellists.
The 3/4-size cello bow is 26 inches long. Players who use a 3/4-size cello (back length of 27 inches) use a 3/4-size bow. This bow size is usually for younger players who are not yet completely comfortable with a full-size bow and instrument.
The 1/2-size cello bow has a length of 24 inches and corresponds to a cello with a back length of 25 1/2 inches. This bow and cello are used by young beginner players who cannot yet play a larger cello.
A 1/4-size cello bow measures 23 inches -- the back length of a 1/4-size cello is also 23 inches. The 1/4-size bow is the smallest bow, but it can be used for an even smaller cello, the 1/8-size. These cellos and bow are typically starter instruments for small children who are learning the basics of the cello.