There are 8 main sizes for the violin. The size refers to the length of the body of the violin, excluding the neck and scroll.
Violin sizes begin at 1/32 and go to 4/4 (full size).
The most common violin sizes are as follows: 1/32, 1/16, 1/10, 1/8, 1/4, 1/2, 3/4, 7/8 to 4/4 or full size.
1/32, generally used by very small children, is the smallest and 4/4 (full size) is the largest, generally used by adults.
You can learn more about how to measure which violin size is right for you here.