The picture below shows how the violin increases in size, from the smallest (1/16th) to the largest (4/4, or full size).
A good way to estimate the correct size violin for your son is to measure the length of his arm from the neck to the middle of his palm with the left arm extended. Then, you may follow the violin sizing guide pictured below.
Another way to assess fit is to have him extend his left arm and grasp the scroll of the instrument. Usually, if a student can comfortably grasp the scroll, as pirctured above, then the violin should be the right size.
Students usually stay in each size for a year or two. Because children grow so quickly and unpredictably, it is important to reasses fit frequently. Using a violin that is too small will cramp both the left hand and the bow arm. However, a violin that is too large can cause strain and injury to muscles and joints as the student is forced to extend the reach of the left hand beyond its appropriate limit.
At 9 years old, your son may need a 3/4 size instrument. However, depending on his height and the length of his arms, the appropriate size for him will likely range from 1/2 size to full size.
I like to tell students that "the violin is an acoustically perfect instrument." What this means is that a full size violin, at 14'' in length, is ideally configured to offer maximal projection and body of tone. Unfortunately, any violin either smaller than or larger than a full size instrument is not acoustically perfect. In general, the smaller the violin, the smaller the sound. This puts the young beginner at an immediate disadvantage: no matter how well he plays the violin, his 1/2 size fiddle will never sound as good as a full size instrument of similar quality. However, the closer in size he gets to the full size, the better his instrument should sound.
But not all small violins are built alike!! You can give your son a better experience by renting or purchasing a high quality small instrument. While it may never sound as good as a full size of comparable quality, it can certainly sound better than the small instruments played by many of his peers.
The key is to rent or purchase the instrument from a reputable shop that carries hand-carved small instruments. In the last few years, affordable hand-carved instruments have become available in violin shops across the United States. Thus, factory-made violins, along with their inferior sound, should be relegated to the past.
Finally, once you know what size he needs, your son should several different instruments before making a final decision. A shop may offer several violins of the same size and "model." But even these are not identical! Every instrument sounds different. Not even two instruments by the same maker sound alike. As a teacher, I like to assist in selecting an instrument, or at least give a final thumbs up before a student rents or (especiially) buys an instrument.
