I ordered a small which should have been the correct size based on measuring My Wife's head.
The helmet is too narrow side-to-side, and too long front-to-back.
Other brands of helments fit My Wife very well, but the Ember seems to have a different shape that just doesn't fit.
Previously owned a less expensive Bell that didn't fit well. design was such that it irritated part of my scalp. This one gits great, feels great and is much cooler. Thanks BTD for a great deal on a great helmet!