I purchased #16. I wear a 7 or 71/2. The pandemic, jeesh. I?d size down. The sound is clear and I can hear it over my dramatic panting during a workout. As far as fit goes, this is a tough one. (one charge a day is all I need). They don?t hurt my ears or head when I do so that?s a huge plus. A few tips on how best to install these. If I buy them again I would stick to same size as next size up might go to loose.