Dog collar size calculator

What to measure, and where

Measure where the collar actually sits: the base of the neck, not up behind the ears. On a dog that already wears one, the easiest marker is where the collar has flattened the coat. Keep the tape snug with room for two fingers underneath — that two-finger gap is the difference between a collar that stays on and one that chafes.

There is one important exception in this dataset. PetSafe sizes its martingale by “neck (top of neck, directly behind the ears)”, and notes that the measurement is the collar at its fully tightened size. A martingale has to pass over the head and then draw in, so the measuring point is different from a buckle collar’s.

Coat matters more here than anywhere else on this site. A thick double coat can add real inches to a neck reading, and a collar measured over winter coat can be loose in summer. Measure against the body, parting the coat if you need to, and check the fit as the coat changes. The measuring guide has a diagram.

How the answer is worked out

For each of the 29 published sizes, the calculator asks whether your measurement is inside the neck range that maker prints. Nothing else. The ranges were transcribed from each maker’s own website on Nov 4, 2026, not from retailer listings, which routinely carry out-of-date charts.

Anything within 1 in of either edge of a size, or inside two sizes at once, is reported as between sizes with both shown. Collar charts overlap more than harness charts do, because an adjustable collar is designed to cover a span, so landing in two sizes is normal rather than a problem.

If you give a weight and no neck measurement, the calculator can only use the 1 of 7 charts whose makers print weight, and it labels those answers by weight only, less reliable. Blueberry Pet prints weight as maximums rather than bands, so those rows take their lower bound from the row above, which is how the table reads; the calculator flags that too.

Why brands disagree

No standard exists, so each maker drew its own bands. The clearest illustration is that Ruffwear does not use letters at all: it labels its collar sizes by the neck range itself, so its chart reads “11"-14"” where another maker’s would say Small. That is a better label, and it is the exception.

The charts also differ in what they are measuring. Max and Neo publishes two products that look interchangeable and are not: its martingale chart gives neck sizes, while its buckle collar chart gives the length of the collar itself. Only the neck chart is used here, because collar length and neck circumference are different numbers.

Note: 2 Hounds Design uses a separate chart, with neck and head measurements, for its slip-on martingales. Only its buckle-collar chart is in this dataset, so if you are buying a slip-on from them, check that chart directly on its product page.

What to do when you are between sizes

None of the 7 collar makers in this dataset publishes between-sizes advice, so this site offers none. A rule of thumb invented here could easily be backwards for a particular product, and the row tells you to check the maker’s chart instead.

What can be said comes straight off the charts. Some makers draw ranges that genuinely overlap, so a band of measurements sits in two of their sizes at once; others end each size exactly where the next begins, so a measurement has one home and only the shared edge is ambiguous. Which one you are dealing with changes what “between sizes” even means:

• Ruffwear Front Range CollarRuffwear’s sizes do not overlap: each one ends where the next begins, so no measurement sits in two of them. Check the maker’s chart.
• Blueberry Pet Classic Solid Color Adjustable Dog CollarBlueberry Pet’s sizes overlap at 14.5 to 16 in and 18 to 20 in, so a measurement in that band genuinely sits in two sizes at once.
• PetSafe Martingale CollarPetSafe’s sizes overlap at 10 to 16 in, so a measurement in that band genuinely sits in two sizes at once.
• Max and Neo Martingale All Nylon Dog CollarMax and Neo’s sizes overlap at 19 to 20 in, so a measurement in that band genuinely sits in two sizes at once.
• Wild One Waterproof Dog CollarWild One’s sizes overlap at 8 to 10 in, so a measurement in that band genuinely sits in two sizes at once.
• 2 Hounds Design Side Release (Buckle) Collar / Buckle Martingale2 Hounds Design’s sizes overlap at 10 to 11 in and 16 to 18 in, so a measurement in that band genuinely sits in two sizes at once.
• Carhartt Dog CollarCarhartt’s sizes do not overlap: each one ends where the next begins, so no measurement sits in two of them. Check the maker’s chart.

Where the ranges overlap, both sizes are shown and the maker has decided that band belongs to both. Where they do not, you are on a shared edge and the maker’s own chart is the only thing that settles it.

A martingale is a different shape of problem. It has to pass over the head before it draws in, so the head is involved as well as the neck, and the published measurement means something different: PetSafe sizes its martingale by “neck (top of neck, directly behind the ears)” and states that the figure is the collar at its fully tightened size. Read that chart on its own page rather than against a buckle-collar range.

Two worked examples

Both computed by the same code the calculator runs, against all 7 charts.

The second is a good demonstration of why the letters are meaningless: at 20 in the same dog is at the top of one maker’s Medium, in the middle of another’s Large, and at the bottom of a third’s XL.

Puppies

Buy for the neck you can measure now. A collar bought large enough to last a year is a collar a puppy can back out of, and the two-finger check is the one to repeat: if a third finger fits, it is too loose.

Re-measure monthly while the dog is growing. Collars are cheap relative to crates and harnesses, and most owners go through two or three before a dog is full grown.

Common questions

Where do I measure my dog’s neck for a collar?

Where the collar actually sits, which is the base of the neck rather than up behind the ears. If your dog already wears one, measure where it has worn the coat. Keep the tape snug with two fingers' room underneath. One exception: PetSafe sizes its martingale by the measurement "neck (top of neck, directly behind the ears)", because a martingale has to pass over the head.

How many collar charts does this check?

All 7 of them, which between them publish 29 sizes. They are transcribed from each maker's own site, not from retailer listings. Ruffwear is the one that does not use letters at all: it labels its collar sizes by the neck range itself.

What if my dog is between two collar sizes?

Within 1 in of the edge of a size, or inside two at once, is shown as between sizes with both options. No collar maker in this dataset publishes between-sizes advice, so the row tells you to check the maker's chart rather than offering a rule of thumb. Adjustable collars overlap by design, so the two sizes often both work; the smaller one usually sits better on a dog that has stopped growing.

Can I use my dog’s weight to pick a collar?

Barely. A neck is a circumference and weight is not. Two collar makers here print weight as a rough guide and the rest do not, so a weight-based answer is labelled "by weight only, less reliable" and should be treated as a shortlist, not a size.

Is a collar size the same as a harness size?

No, and they are not even measuring the same thing: a collar is sized on the neck and a harness on the chest girth. A dog can be a Large in one brand’s collar and a Medium in the same brand’s harness without anything being wrong.

Where to go next

• How to measure your dog — where the tape goes, with a diagram.
• Every collar size chart side by side— the raw charts, filterable by measurement.
• Dog harness size calculator — the same tool for a harness.
• Dog crate size calculator — the same tool for a crate.

Measure your dog. Everything here is a published chart read against your number: a starting point, never a promise of fit. And this is not veterinary advice — sizing says nothing about whether a piece of equipment suits your dog’s health, breathing or behaviour. Full disclaimer.