Measuring Your Dog for a Perfect Fit * 1.How to measure your dog? Don't buy a particular size because that is what you always buy in a pet shop or online store. 3.If any of the measurements are 'between' two sizes, choose the larger size. If your measurements are toward the upper end of the range given for a particular size, you may also want to choose the larger size, as you may also wish to do for heavily coated dogs to accommodate all that fur. 7.Take each measurement a bit loosely.