* The chin strap is the length from under one ear (across the chin) to the other ear.
Size Weight Head Strap Chin Strap XXS up to 2 lbs 3-9 inches 2-3 inches XS 2-10 lbs 5-13 inches 3-7 inches Small 9-25 lbs 12-20 inches 4-8 inches Medium 20-60 lbs 15-25 inches 5-11 inches Large 50-100 lbs 18-30 inches 6-15 inches