What size of violin does my child need?

A lot of people must be asking the same thing, either for their young beginner, or for a student who has grown a bit bigger.
Either way, it's important to answer this question correctly. A properly-fitting violin will help ease a student's studies, making the instrument easier to handle and hold.
We're actually lucky that violins come in various sizes! An octave on a piano is always an octave, no matter how small the hands attempting to play it! There are seven typical "fractional" sizes for violins, from smallest to largest: 1/16, 1/10, 1/8, 1/4, 1/2, 3/4 and full-size. I'm going to give you instructions on how to measure your child, and then a little chart to determine what size instrument you need.
First, you need to measure the child's arm, from his or her neck to the line on the wrist where his or her hand starts.

Have your young student stand upright, holding out his or her left arm, palm facing up. Gently measure the distance from the left side of the neck out to the line where his or her wrist meets the hand (in inches or centimeters). At left is a picture of that natural line at the wrist, which have I darkened with pen, so that you can see what I mean. You can use a tape measure or a yardstick.
The chart below will tell you what size violin is appropriate. I find these measurements to be extremely accurate -- more so than the old trick of having the child attempt to grasp the scroll. If you are a private teacher or a school teacher, you easily can make your own "Fiddle Stick," with a yardstick (or meterstick) and some permanent markers. (If you are feeling like collecting some goodwill karma, make one for your local overworked and underpaid public school teacher!)
Measurements in Inches:
1/16 size: 13 1/4 inches or less
1/10 size: 14 1/4 inches
1/8 size: 15 1/4 inches
1/4 size: 17 1/4 inches
1/2 size: 19 inches
3/4 size: 20 1/2 inches
Full size: 21 1/4 inches
Measurements in centimeters:
1/16 size: 33 1/2 cm or less
1/10 size: 36 cm
1/8 size: 38 1/2 cm
1/4 size: 44 cm
1/2 size: 48 1/2 cm
3/4 size: 52 cm
Full size: 54 cm
GUIDELINES: Always err on the side of getting the smaller violin. It is tempting to get the bigger size, figuring, "Oh, (s)he'll grow into it," but it is extremely frustrating for a child to work with an unwieldy violin that is too big, and importantly, too heavy! You want the child to feel in control of the violin. A too-big violin may actually hurt to hold because of its weight, and it may throw off the mechanics of playing because of its size.
If you are getting a violin for the first time, all the best on your new musical journey! If you are up-sizing, enjoy the new (likely improved) sound of a bigger fiddle