Measure a tee you already love. Lay it flat, measure from armpit to armpit for the chest, and from the highest point of the shoulder to the hem for the length. Compare those numbers to the Windbar chart. That's the closest you'll get to a perfect match without trying it on.

Keep the tags on when it arrives. Try it on over the layers you plan to wear. Move around. Raise your arms. That's the real test.