How do you size a dog harness? Measure the chest and check the chart

Harness sizes are not standard, so "medium" can mean very different things. Measure your dog's chest once, then check it against the exact size chart with this little fit checker.

Then work through a six-point fit check on the dog: fingers under the straps, free shoulders, no rubbing, no backing out. Includes the one-versus-two-finger advice from different sources, how to introduce a harness with treats, and when to ask a vet.