The two main measurements you want to focus on are your dogs chest and back length. The most important measurement is your dogs chest measurement in most cases.
You can also easily convert inches to centimeters or vice versa by using the chart below:
How to Measure Your Dog:Have your dog sit in front of you and use a soft tape measure to measure the area around its neck that the collar will sit. Loosely measure the neck where the collar would normally sit sliding two fingers between the dog’s neck and measuring tape. Adding the two fingers should make the collar size about 2″ larger than the dog’s neck size (maybe closer to 1″ on very small dogs.) To measure your dog appropriately, measure the girth around your dog’s chest, just behind the front legs. To measure your dogs length take a soft tape measure from the bottom of your dogs neck and measure until the end of your dogs back. Note, on some clothes they will not stretch past your dogs back legs – so item lengths may seem short, therefore we suggest also using breed recommendations along with measurements.
Dog Breed Sizing