These Jerseys are a slam dunk for days at the beach, summer strolls, or early morning walks!
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For sizing, you should check the specific chart referenced above, but you may find the following a helpful guide for a quick assessment ( inches refer roughly to length measurements):

X-Small: 7" (2.5-5 lb) Small: 9" (5-8 lb) Med: 10" (8-12 lb) Large: 12" (13-20 lb) X-Lrg: 13" (20-31 lb)