When measuring your dog for a harness, you'll need two measurements - one for the neck and one for the waist (also known as the girth). Using a tape, measure the base of the neck and the circumference of the chest. Be sure to add a couple of fingers underneath to allow a little extra room - you don't want the tape to be too tight. 

In the guide below we've added typical breeds based our experience, however we'd always recommend measuring your pup where possible.