Sizing for Discovery tails are based on a couple of different measurements:Where to measure yourself for your discovery tail:Waist (where you'd like the tail to hit on your torso)Hips/butt (around the widest part, typically right around the pelvic bone)Length (from floor to where you'd like you tail to hit on your torso)2. Choose the size that is closest to your smallest measurement and make to size DOWN if in between sizes. For example, if your waist measures for a small and your hips measure for a medium, choose the small.Our tails have vertical stretch as well as horizontal stretch so don't worry taller mers, if the length of any given size is a bit short, they do have a few extra inches of vertical stretch.For any sizing questions, please don't hestiate to email the team at info@finfolk.com with the above measurements.