Finding a violin bow that's the right size is as important as finding the perfect size violin. By following these steps, you can find the proper size for both. According to professional violin and viola teacher Rhiannon Schmitt of Fiddleheads, "The most important thing in deciding the correct size is that the student can comfortably play the instrument in tune. Fourth-finger (or pinky) reach and intonation may be the deciding factor."
Determine the age of the player. In most cases, adults, teens and small adults play full-size violins and thus full-size (29.5-inch) bows. Write down the player's age on the paper.
Measure the length of the player's arm by placing the measuring tape on the left side of the base of the neck and going the length of a straight left arm to the base of the fingers. Write this measurement on the paper as the "palm measurement." This measurement indicates the maximum size, usually used for a rapidly growing child.
Using the same outstretched arm, measure again from the left base of the neck and measure to the wrist. Write this on the paper as the "wrist measurement." This measurement results in a comfortable size.
Compare the results that you have written with the chart provided below to guide you to a correct bow size (other than for adult or small teen): A child aged 9 to 12 with an arm length of 21.5-22 inches will probably need a 3/4 violin with a 27-inch bow. A child aged 7 to 9 with a 20-inch-long arms will probably need a 1/2-size violin and a 24.5-inch bow. For children aged 5 to 7 with an arm length of 18 to 18.5 inches, a 1/4-size violin and 22.5-inch bow will probably be just right. And a 1/8-sized violin and a 19.25-inch bow is probably the right fit for children aged 4 to 6 with 16.5-inch-long arms.
When measuring the arm, make sure it is completely straight and not bent at all.
These sizes are guidelines and for best results you should use a violin and bow to find the best fit. Also, consult a violin dealer or other professional when available.