Measuring your dog is the best way to get a harness to fit your baby. 
Also, if your dog's chest/neck measurement is at the bottom or top of the size, I can cut/add the additional length of the harness FOR FREE. 

For the harness, please provide me the  "Neck base" and the "chest girth" measurements.
Please notice that "Neck base" and "neck girth" are different.
When I make your dog's harness, I always add additional 1 inch to the neck base measurements.  
EX: If your dog's neck base is 14", I will make 15" on the harness - To let your dog wear the harness comfortably.
Hence, please measure your dog snuggly. Otherwise, the harness will be made too big.

Here's the photo to show you how to measure your dog!

If you have an old harness with the same style as my harness, and you think it fits your dog well. You can measure the old harness too. I then can make my harness has the same measurements as your old one. :)