Tunic sizing is based upon measurements of the individual garment while it is laying flat, not upon S, M, L. They are meant to fit a variety of body types and can be worn close to the body or in a more loose, drape-y silhouette. Measure around the fullest part of your bust to determine how the tunic will fit you (double the width measurement of the tunic to see how much wiggle room you'll have.) Length measurements are taken from the neckline to the bottom hem.
Please contact me if you have questions about the fit of a specific garment.
Also, I am happy to make custom pieces, so please contact me if you would like a garment with different measurements!