What size harness does a Mastiff need?
The breed standard puts a Mastiff at 54–100kg (119–220lb). Published weight guidance gives a shortlist at 5 of 12 charts, including 4 with only one candidate. Chest girth is still needed at every chart.
Measure your dog’s chest
Enter a tape reading to compare the published girth ranges. Weight only helps choose between sizes that already cover that measurement. See where to put the tape.
Around the chest, just behind the front legs. Measuring guide.
Optional. Each fully grown dog of a named breed adds to that breed’s measured chest range, published on its breed page once twenty are in.
Type the chest girth and the size appears for all 12 harnesses — Julius-K9 · Ruffwear · PetSafe · Kurgo · Blue-9 · Rabbitgoo · Puppia · PetSafe 3 in 1 · Dog Friendly Co · PawSafe · Wonder Walker · Top Paw — with where your dog sits inside each size.
Before you order — the two-finger rule · full measuring guide
- Measure the deepest part of the ribcage, just behind the front legs, with the dog standing.
- Two fingers should slide flat under any strap. A whole hand means it is loose enough to reverse out of.
- Snug against the coat, not pulled tight through it — and re-check after a groom.
Ranges are transcribed from each manufacturer’s own chart. See the full conversion chart or how we check these numbers.
Fitting a harness on a Mastiff
The Mastiff is a massive, heavy-boned dog with an exceptionally wide and deep chest. Adults vary significantly in total mass, and the neck circumference often matches the head size.
An escape-resistant design with a secondary belly strap can be useful for security on such a large animal. The harness must have extra-wide straps to distribute the dog's immense weight comfortably across the chest.
Measured a fully grown Mastiff? Enter the chest in the tool above and set “Fully grown”. At 20 dogs this page shows a range from owners’ actual tape readings.
The weight shortlist matches Saint Bernard. The same weight candidates can cover dogs with different chest measurements. Use your own tape reading to choose from the charts.
Weight guidance: a shortlist to check
These labels come from overlap between the breed’s adult weight standard and each chart’s weight guidance. They do not establish your dog’s chest size or guarantee a fit.
| Brand | Weight candidates | What it means |
|---|---|---|
| Julius-K9 Maker’s chart · checked 2026-08-19 | 3 or 4 | Published weight guidance overlaps the breed standard at 3, 4. Measure your dog's chest to check which girth ranges cover it; weight alone cannot choose a size. |
| Ruffwear Maker’s chart · checked 2026-10-04 | measure | Ruffwear publishes no weight guidance on this chart. Measure your dog's chest to compare its girth ranges. |
| PetSafe Maker’s chart · checked 2026-08-19 | Extra Large | Only Extra Large has published weight guidance overlapping the breed standard. A shortlist of one still needs your dog's chest measurement; weight does not confirm a fit. |
| Kurgo Maker’s chart · checked 2026-08-19 | no weight overlap | None of this chart's published weight guides overlap the Mastiff standard's 54–100kg range. This does not rule out a chest-chart match: measure the girth and check the maker's guidance. |
| Blue-9 Maker’s chart · checked 2026-08-19 | measure | Blue-9 publishes no weight guidance on this chart. Measure your dog's chest to compare its girth ranges. |
| Rabbitgoo Maker’s chart · checked 2026-08-28 | measure | Rabbitgoo publishes no weight guidance on this chart. Measure your dog's chest to compare its girth ranges. |
| Puppia Maker’s chart · checked 2026-08-28 | measure | Puppia publishes no weight guidance on this chart. Measure your dog's chest to compare its girth ranges. |
| PetSafe 3 in 1 Maker’s chart · checked 2026-10-04 | Large | Only Large has published weight guidance overlapping the breed standard. A shortlist of one still needs your dog's chest measurement; weight does not confirm a fit. |
| Dog Friendly Co Maker’s chart · checked 2026-10-04 | measure | Dog Friendly Co publishes no weight guidance on this chart. Measure your dog's chest to compare its girth ranges. |
| PawSafe Maker’s chart · checked 2026-10-04 | XL | Only XL has published weight guidance overlapping the breed standard. A shortlist of one still needs your dog's chest measurement; weight does not confirm a fit. |
| Wonder Walker Maker’s chart · checked 2026-10-04 | X-Large | Only X-Large has published weight guidance overlapping the breed standard. A shortlist of one still needs your dog's chest measurement; weight does not confirm a fit. |
| Top Paw Maker’s chart · checked 2026-10-04 | measure | Top Paw publishes no weight guidance on this chart. Measure your dog's chest to compare its girth ranges. |
Ruffwear, Blue-9, Rabbitgoo, Puppia, Dog Friendly Co, Top Paw publish no weight guidance on these charts. Their girth ranges are still available in the finder above.
Kurgo has no published weight guide overlapping this standard. That alone does not exclude a chest-chart match; check your dog’s measurement and the maker’s guidance.
How to measure a Mastiff
Use a long measuring tape to find the circumference of the massive ribcage at its widest point, ensuring the dog is standing.
Take a soft tape right around the deepest part of the ribcage, just behind the front legs. Keep it snug against the coat rather than pulled tight — you should be able to slide two fingers under it. That single number, the chest girth, is what every brand on this page sizes by. Weight is only ever a tie-breaker. The full measuring guide covers the mistakes that send harnesses back.
Other giant breeds
- What size harness does a Rottweiler need?
- What size harness does a Great Dane need?
- What size harness does a Bernese Mountain Dog need?
- What size harness does a Newfoundland need?
- What size harness does a Akita need?
- What size harness does a Saint Bernard need?
- What size harness does a Great Pyrenees need?
- What size harness does a Bullmastiff need?
Weight range from the breed standard, read 2026-08-25. Weight candidates come from each manufacturer’s published chart. The finder uses your measured chest girth; it does not estimate a chest measurement from the breed.