How do I measure my dog for a harness?

Taking the measurement

1. Stand the dog up squarely. A sitting or lying dog gives a reading that is wrong in both directions, because the ribcage changes shape.
2. Wrap the tape around the deepest part of the chest, immediately behind the front legs. This is girth, and it is the primary number.
3. Measure neck circumference where a collar would sit, lower on the neck than you expect.
4. Measure back length from the base of the neck to the base of the tail, needed for step-in and vest styles.
5. No tape measure: use string, mark where it overlaps, then lay it flat against a ruler.

Check the size chart for the specific harness rather than assuming a medium is a medium. Sizing is not standardised between manufacturers, and a dog can be a small in one brand and a large in another.

Checking the fit once it is on

• Two fingers should slide flat under any strap. More than that and the dog can back out of it, less and it restricts.
• The girth strap sits behind the ribcage, not in the soft belly and not jammed into the armpits. Rubbing behind the elbows is the most common fitting fault.
• Front-clip harnesses should sit level across the chest. A ring that slides to one side means the harness is loose or the wrong shape for that dog.
• Watch the dog walk for a full minute. Fit faults show as a shortened front stride rather than as obvious discomfort.
• Recheck monthly on a growing puppy, and after any significant weight change in an adult.

When in doubt

Size up. A slightly loose harness that is adjusted down beats a snug one with no room left, and a harness that becomes tight when the dog leans into it is one that will chafe. For flat-faced breeds, a harness is not a preference but the safer default, since a collar puts pressure on an already compromised airway.