What size harness does a Border Collie need?
The breed standard puts a Border Collie at 12–20kg (26–44lb). Weight alone settles the size at 1 of the 5 brands. 2 brands size by girth only and are left blank rather than guessed.
What that weight means at each brand
| Brand | Size | What it means |
|---|---|---|
| Julius-K9 | Mini or 0 | The breed's weight range spans 2 Julius-K9 sizes (Mini, 0), so weight alone cannot pick between them. The chest measurement decides. |
| Ruffwear | measure | Ruffwear sizes by chest girth only and publishes no weight guidance, so a Border Collie's weight cannot be converted to one of their sizes. Measure the chest and the tool above will answer it exactly. |
| PetSafe | Small/Medium or Medium or Medium/Large | The breed's weight range spans 3 PetSafe sizes (Small/Medium, Medium, Medium/Large), so weight alone cannot pick between them. The chest measurement decides. |
| Kurgo | Medium | Every Border Collie in the breed's weight range falls in Kurgo Medium. |
| Blue-9 | measure | Blue-9 sizes by chest girth only and publishes no weight guidance, so a Border Collie's weight cannot be converted to one of their sizes. Measure the chest and the tool above will answer it exactly. |
Blank entries are deliberate. Ruffwear and Blue-9 publish no weight guidance to convert, and printing a size anyway would be a guess dressed as an answer.
Now measure, and get the exact size
A breed weight range covers both sexes and every build, which is why it spans more than one size almost everywhere. One measurement replaces all of it. Wide weight range; working lines run leaner than show lines.
Measure right around the deepest part of the ribcage, just behind the front legs.
6 size ranges overlap here. The marker shows where your dog falls inside each one — nearer the middle means more adjustment room either way.
How to measure a Border Collie
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.
Why the answer is a range, not a number
Every page that hands you one size for a Border Collie is hiding the same problem: the breed standard covers a 67% spread in weight between the lightest and heaviest adults, and girth varies more than weight does. Two Border Collies on the same scale reading can be a size apart. The honest answer is the shortlist above plus the tape.
Other medium breeds
- What size harness does a French Bulldog need?
- What size harness does a Bulldog need?
- What size harness does a Beagle need?
- What size harness does a Dachshund (Standard) need?
- What size harness does a Pembroke Welsh Corgi need?
- What size harness does a Siberian Husky need?
- What size harness does a English Springer Spaniel need?
- What size harness does a Brittany need?
Weight range from the breed standard, read 2026-08-25. Sizes come from each manufacturer’s own published chart — nothing on this page is estimated or averaged between brands.