How to choose the right dog collar size
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Getting a dog collar size wrong is easy to do and easy to fix — if you know what to measure and what to look for. Here is the complete guide, including how to measure, what a proper fit feels like, and how collars should sit on different breeds.
The short version: Measure your dog's neck at the widest point, then add 2–3cm. Fit it so you can slide two fingers comfortably underneath. Too loose and it slips off; too tight and it causes pressure and discomfort. Re-check fit as puppies grow.
1. How to measure your dog's neck
You need a soft tape measure or a piece of string and a ruler. Measure around the widest part of your dog's neck — this is usually just below where the neck meets the shoulders, not high up near the ears. Keep the tape snug but not tight. Write the measurement down.
Add 2–3cm to that measurement to give yourself a working range. This is your collar size. If a collar lists a range, you want your dog's measurement to sit in the middle of that range so there is room to adjust smaller or larger.
2. The two-finger rule
Once the collar is on, slide two fingers underneath it flat against your dog's neck. Both fingers should fit with light resistance. If you can fit three fingers easily, it is too loose. If you struggle to fit one, it is too tight.
This rule works for flat collars on adult dogs. For puppies, the same principle applies, but you should check fit every two to three weeks as they grow — a collar that fits well at eight weeks can be dangerously tight by twelve.
3. Breed considerations
Wide-necked breeds (Labrador, Rottweiler, Staffordshire Bull Terrier): measure carefully at the thickest point. These dogs often need a wider collar to distribute pressure evenly — a narrow collar on a thick neck can cause discomfort during leash pressure.
Narrow-headed breeds (Greyhound, Whippet, Saluki, Afghan Hound): the neck is often wider than the head, which means a standard collar can slip forward over the skull. These breeds typically need a shaped or martingale collar designed specifically to prevent this.
Flat-faced breeds (French Bulldog, Pug, English Bulldog): anything that adds pressure to the neck increases breathing strain. A harness is generally a better choice than a collar for lead walking. A collar for ID tags is fine; a collar as the primary walking connection is not.
4. What a well-fitting collar looks like in daily use
A correctly fitting collar should sit flat around the neck without bunching or gaping. When your dog shakes their head or rolls on the ground, it should stay in place without rotating. When you attach a lead and your dog pulls, the collar should not move up toward the ears or down toward the chest.
If you notice redness, hair loss or skin irritation under the collar, it is either too tight or moving too much — both are fixation problems. Check the fit and, if the problem persists with correct sizing, consider whether the collar material is right for your dog's skin and coat type.
5. When to replace a collar
Replace a collar when: the hardware (buckle, D-ring) shows rust or cracking; the material is fraying around the edges or near the hardware; the collar no longer sits flat and holds its shape; or your dog has outgrown it. A collar is a safety item — it is what holds your dog's ID tag and connects to a lead. It should be in good condition at all times.