How to Measure a Dog for a Harness: A Simple Fitting Guide
A well-designed harness can still fit poorly if the wrong size is chosen. A harness that's too loose can shift out of position or make it easier for a dog to back out of it; one that's too tight can create pressure, rubbing or restrict comfortable movement. Measuring your dog properly is how you arrive at the right starting size, before checking the actual fit on your dog.
If you haven't yet decided between a harness and a collar in the first place, our guide on Harness vs Collar: Which Is Better for Walking Your Dog? covers that decision separately.
What you'll need
- A soft, flexible measuring tape — not a rigid DIY tape
- Your dog standing naturally on a level surface
- The sizing guide published by the manufacturer of the specific harness you're considering
Harness designs differ enough that there's no single measurement system that applies to every harness. Two harnesses labelled "Medium" from different manufacturers can fit differently, so always check the actual sizing chart for the harness in question rather than assuming your measurements translate directly across brands.
1. Measure the chest girth
Wrap the tape around the broadest part of the ribcage, just behind the front legs — the chest girth measurement most harness manufacturers ask for, shown in the photo above. Keep the tape flat against the coat and comfortably snug, without compressing the body. Note the measurement in both centimetres and inches if the manufacturer's chart uses a different unit than you're used to.
2. Check whether the harness requires a neck measurement
Not every harness is sized from chest girth alone. Some designs also need a neck measurement, taken around the base of the neck where it meets the shoulders, because of how their straps are cut and adjusted. Check the specific harness's own sizing guide to see which measurements it actually asks for, and take those measurements at the points the manufacturer specifies — don't assume every harness uses the same reference points.
3. Don't choose a size from weight or breed alone
Two dogs of a similar weight, or even the same breed, can have noticeably different chest depths, neck circumferences, ribcage shapes and shoulder structures. A breed or weight chart can give you a rough starting point, but it isn't a substitute for measuring your own dog. Use the actual measurements to choose the size, and treat weight or breed guidance as a cross-check at most.
What if your dog is between sizes?
If your dog's measurements fall between two sizes, check the manufacturer's adjustment range and fitting instructions for each size before deciding. Many harnesses have enough adjustment to comfortably accommodate a dog just outside the midpoint. Don't assume sizing up is automatically the safer choice — a harness that's too large for its adjustment range can shift, rotate or make it easier for a dog to back out. If neither size looks clearly appropriate once you've checked the adjustment range and fitting instructions, check with the retailer or manufacturer rather than guessing.
How should a harness fit?
Measuring only gets you to a starting size. Once the harness is on, fit it and observe your dog during normal movement. Check for:
- Excessive side-to-side movement
- Rubbing near the front legs or armpits
- Pressure around the neck
- Obvious restriction of shoulder movement
- Obvious pressure points
- Excessive looseness that could allow the dog to back out
You may have come across the "two-finger rule" — being able to fit two fingers between the harness and your dog's body. It's a rough fitting check at best, not a fixed rule: coat thickness, strap width, harness construction and the manufacturer's own fitting instructions all affect what a correct fit actually looks like on a specific harness.
Signs a harness may be too tight
Watch for rubbing, visible indentation in the coat or skin, pressure points, restricted movement, or signs of discomfort while the harness is worn. A dog reacting to a new harness isn't automatic proof that the fit is wrong — many dogs need time to adjust to wearing any new equipment — but rubbing, indentation or restricted movement that persists is worth acting on.
Signs a harness may be too loose
A loose harness can show up as excessive strap movement, the harness rotating around the body as the dog walks, large visible gaps between the straps and the body, or legs and shoulders starting to move through parts of the harness where they shouldn't. In the most obvious cases, a harness that's too loose creates a real risk of the dog backing out of it entirely.
Check shoulder movement
A harness can be securely attached and still interfere with how your dog moves. Watch your dog walk normally and check that the straps aren't obviously restricting the front legs or shoulders with each stride. Secure isn't the same as correctly fitted.
Puppies need to be measured again
A growing puppy's measurements change, so check the fit regularly rather than assuming a harness bought a few months ago still fits. Adult dogs aren't exempt either — a meaningful change in body weight, body condition or coat (a heavier winter coat, for example) is a reasonable prompt to remeasure and recheck the fit.
Simple fitting checklist
- Measure according to the exact harness manufacturer's instructions.
- Choose the size from actual measurements rather than breed alone.
- Adjust all relevant adjustment points.
- Check for excessive movement or pressure.
- Observe the dog walking normally.
- Recheck the fit after use.
Harnesses to explore
If you're shopping for a harness to measure against, here's what's currently available from Prydea:
Standard Dog Harness — from £35.95. Adjusts at both the neck and chest, with published measurements for every size.
Conclusion
The measurement is only the starting point. A sizing chart tells you where to start; how the harness actually sits and moves on your dog tells you whether it's the right one. Take the time to check the fit properly once the harness arrives, and check with the manufacturer if you're ever unsure between two sizes.