The violin and viola are similar in look but have these differences:
1. The strings – The violin has strings – E, A, D, G. The viola has strings A, D, G, C. Do you notice how they both have three strings in common? So the difference is that the viola has a “C string,” instead of the “E string,” while the violin has the “E string” instead of the “C string.” Because of this difference the viola is lower in pitch. One thing you can purchase is a 5-string violin which accommodates playing violin and viola music. If you are interested in a high quality 5-string, I highly recommend my Damiano violin (available in both 4 and 5 string).
2. The size – A full size viola ranges in size from 15″-17.5.” The most common size people play is a 16″ size, while all violins are 14″. Finger spacing on a viola is wider than a violin.
3. The Bulkiness – The ribs on a viola are wider than a violin. This gives the inside a little bit more space to accommodate a deeper sound.
4. The music – Viola music is in alto clef while violin music is in treble clef. The note at the bottom of the music staff in trebel clef mode is a D. If you are reading the same note in viola (alto) clef, it is an E. One of the hardest things to get used to when switching from the viola to the violin is getting used to reading the music clef.
Regarding technique of playing, both instruments are very similar. You have to get used to the length of playing the viola regarding the finger spacing and reach, but other than that, it isn’t that difficult to transition over. Getting used to the music reading is the most difficult part, but usually doesn’t take longer than a few months to get used to.
Here is a video of both instruments being played. Notice how the viola is more the harmony while the violin is more the melody. The viola is deeper than the viola.