A harness that's too loose slips off, one that's too tight pinches. For a growing puppy, finding the right size is a little trickier than for an adult dog. This guide gets you there in a few minutes, and tells you exactly when to size up.
What you'll need
A flexible measuring tape (or a piece of string and a ruler) and a few minutes of your puppy's patience, a handful of treats helps.
How to measure the right size in 3 steps
- Chest girth. Measure around the widest part of the ribcage, just behind the front legs.
- Neck girth. Measure loosely around the base of the neck, where a collar would normally sit.
- Compare with the size chart. Check our size guide for exact measurements per harness.
Plan for growth
A puppy can grow significantly in just a few weeks. Choose an adjustable harness with room to grow in multiple directions, and recheck the fit every 2 to 3 weeks. A good rule of thumb: you should be able to slide two fingers flat between the harness and the skin, no more, no less.
How to measure accurately (and avoid the wrong size)
- Measure while your puppy is standing calmly, not right after running or playing, since the chest expands differently then.
- Don't pull the tape tight. Loose, but not loose enough to slide.
- Measure twice and take the average if the results differ slightly.
- Does your puppy have a thick coat? Measure over the fur, since the harness sits over it too.
What to avoid
- Don't buy a bigger size for your puppy to grow into. A harness that's already too loose can shift or even slip off during a walk.
- Don't go by collar size. Neck girth and chest girth aren't in a fixed ratio to each other, especially not in puppies that are still growing.
- Don't skip rechecking just because the harness still seems to fit. Puppies grow in spurts, not evenly.
- Don't ignore red marks or chafing, even if they look minor. That's a sign to size up right away.
Frequently asked questions
What if my puppy falls between two sizes?
Choose the smaller of the two sizes, as long as the harness has enough adjustment room to grow into.
How often should I recheck the size?
Up to around 8 months, we recommend checking the fit every 2 to 3 weeks. Larger breeds often grow faster and deserve a slightly more frequent check.
What are signs the harness is too small?
Red marks, chafing, or a harness that's visibly tight against the body with no room for two fingers.
And signs it's too big?
The harness twists around the body while walking, or your puppy can slip a paw through it. That's the time to size down or adjust further.
Do I need to remeasure if I switch brands?
Yes. Size charts differ by brand and model, so a size M in one harness isn't automatically the same in another.
Still unsure? Check our full size guide or shop our adjustable puppy harnesses.
