Our thongs run small, so please size up! Also remember that sometimes your butt size doesn't align with the rest of your clothing size. I usually wear an XS for pants and a small for undies, but I wear a medium for these guys. Here's a chart:

 

US size	UK size	Buttercup size
000 - 00	0 - 2	XS
0 - 2	4 - 6	S
2 - 4	6 - 8	M
6 - 8	8 - 10	L
10	12	XL