Size Guide:S: Neck: 24cm Chest: 40cm Length(back): 26cmM: Neck: 28cm Chest: 48cm Length(back): 30cmL: Neck: 35cm Chest: 53cm Length(back): 33cmXL: Neck: 40cm Chest: 56cm Length(back): 36cmXXL: Neck: 45c, Chest: 62cm Length(back): 39cm **Please measure when your pet is standing up.Length(back):Measure from the base of neck (where the collar would fit) to the base of the tail (not the tip) along your dog’s backbone.Neck:Measure around your dog’s neck using a cloth measuring tape positioned where the collar sits.If you don’t have a cloth tape measure, try using a piece of string and then measure the string with a ruler.Chest:Measure all the way around the biggest part of your dog’s ribcage, generally just behind the withers down and around just behind the front legs and back up the other side.