Dog Collar Size Calculator
Measure for a collar that fits properly, with the right adjustable range and the right width for your dog.
Around the middle of the neck, not tight against the skull.
Used to recommend a collar width.
Collar length to buy
42.1 cm – 45.6 cm adjustable range
- Measured neck
- 40.0 cm
- Recommended width
- 20 mm
You should be able to slide two fingers under the collar comfortably.
- Measure around the middle of the neck, not right at the base of the skull.
- Buy an adjustable collar and aim for the middle of its range, so there is room either way.
- Check the fit weekly on a growing puppy. Collars left too tight are a common and avoidable injury.
- A collar that slips over the ears is too loose. Consider a martingale for narrow-headed breeds like greyhounds.
How this is calculated
Collar sizing is neck girth plus a fitting allowance. The allowance scales with the dog, because two fingers on a Great Dane occupy far more room than two fingers on a chihuahua.
buy range = neck girth + allowance
allowance = about 2.5 cm under 10 kg, 3.5 cm to 25 kg, 5 cm above
width = 10 mm under 5 kg, 15 mm to 12 kg, 20 mm to 25 kg,
25 mm to 40 kg, 38 mm above Measuring properly
- Use a soft tailor tape, or a string you then measure against a ruler.
- Measure the middle of the neck, where a collar naturally sits.
- Keep the tape snug but not compressing the coat, and measure on a standing dog.
- On a thick double coat, measure through to the skin rather than around the fur.
Sources
- Collar sizing is the convention used across common flat and martingale collar ranges, which vary between makers. The two-finger fit test is the check that actually matters.
Buy for the middle of the range
Adjustable collars have a working range, and the useful trick is to buy one whose middle setting matches your measurement. That leaves room to tighten in summer when the coat is thin and loosen in winter, or as a puppy grows, without buying again.
Collar or harness
For identification, a collar. For walking a dog that pulls, a harness, because sustained pressure on the throat is linked to tracheal and thyroid problems, and is a particular concern in toy breeds. Many owners use both: collar for the tag, harness for the lead.
Common questions
How do I measure my dog for a collar?
Put a soft tape measure around the middle of the neck, not tight against the skull, and add room for two fingers. Buy an adjustable collar whose middle setting matches that figure, so there is adjustment in both directions.
How tight should a dog collar be?
Two fingers should slide underneath comfortably on a medium or large dog, one finger on a small one. Tighter than that risks chafing and restricted breathing; looser and the collar can slip over the ears.
What width collar does my dog need?
Roughly 10 mm for toy breeds, 15 mm for small dogs, 20 mm for medium, 25 mm for large and 38 mm for giant breeds. A wider collar spreads pressure, which matters for a dog that pulls, but an over-wide collar on a small neck restricts movement.
How often should I check a puppy collar?
Weekly. Puppies grow faster than owners expect, and collars left too tight are a common and entirely avoidable injury. If you cannot get two fingers under it, loosen it now.
My dog slips out of its collar. What should I use?
A martingale. Narrow-headed breeds such as greyhounds, whippets and salukis can back out of a flat collar because the skull is no wider than the neck. A martingale tightens to a limited, preset point and cannot choke.
Should my dog wear a collar all the time?
It is usually a legal requirement in public with an ID tag. At home, many owners remove it at night or during crating, since collars can catch on crate bars and furniture. Breakaway collars exist for exactly this risk.