What size harness does a Bullmastiff need?
The breed standard puts a Bullmastiff at 45–59kg (99–130lb). Published weight guidance gives a shortlist at 6 of 12 charts, including 6 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 Bullmastiff
The Bullmastiff is a giant breed with a massive, broad chest and a very thick neck. The ribcage is deep and well-sprung, and the dog's overall weight is substantial, requiring heavy-duty components.
A wide, reinforced Y-front harness is necessary to safely manage the dog's mass while keeping the neck free. Look for wide straps and large contact pads to distribute pressure across the expansive chest area.
Measured a fully grown Bullmastiff? 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 Newfoundland. 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 | Only 3 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. |
| 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 | 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. |
| 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.
How to measure a Bullmastiff
Measure at the deepest and widest part of the ribcage, ensuring the tape is level all the way around the dog's large torso.
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 Mastiff 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?
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.