Please use a flexible tailor's style tape measure. I prefer you use inches.
Measurement 1. Chest at the largest circumference behind the front legs Measurement 2. Chest at mid-back Measurement 3. Loin, the narrow circumference at the stomach
Measurement 4. Have your dog stand with his/her weight centered on the front leg closest to you. The front leg should be perpendicular to the level ground: your dog should not have the leg closest to you stepping forward or backward. Start the tape centered on the protruding chest bone and run it under the dog, stopping just behind the front leg, just past the armpit. This measurement is typically 7" for a 50-55lb dog. Measurement 5. From just behind your dog's front legs to where the ribs start to turn upwards at the sternum. This is about 6" for a 50lb dog. Measurement 6. Circumference of neck
Trekking Roll-top Pack Dimensions The best way to know how a particular bag size will look on your dog is to cut out a piece of paper to one of the dimensions below and hold it up to your dog's chest with the leading edge positioned just behind the front leg. Extra-Extra Small: recommended for dog weighing 8-15lb: 6" wide x 4" hang height x 2" thick Extra Small: recommended for dog weighing 15-25lb: 7" wide x 4" hang height x 2" thick Small Size: recommended for dog weighing 25-40lbs: 8" wide x 5" hang height x 2" thick. Regular Size: recommended for dog weighing 40-60lb: 8" wide x 7" hang height x 3.5" thick. Large Size: recommended for dog weighing 60-75lb: 9" wide x 7" hang height x 3.5" thick. Extra Large: recommended for dog weighing 75lbs and up: 10" wide x 8" hang height x 3.5" thick.