A properly fitted dog collar sits high on the neck just below the ears, allows two fingers to slide easily between the collar and the neck, and is snug enough that it cannot slip over the dog’s head.
The easiest mistake is putting the collar on too low or too loose. A collar that hangs near the shoulders gives a dog an easy escape route and can put pressure on the windpipe. Getting the fit right takes a cloth tape measure, about thirty seconds, and one rule you will never forget once you see it work.
What You Need to Measure First
You need a flexible cloth tape measure. A piece of string and a ruler work just as well. Measure around the center of the dog’s neck, a few inches down from the head where the collar will actually sit — not down near the chest where the widest part of the rib cage throws off the number. Pull the tape snug but not tight. That number is your dog’s bare neck size.
Most adjustable collars require you to add 2 inches to that measurement to find the right collar size range. A dog with a 13-inch neck needs a collar that adjusts from about 11 to 16 inches. Always confirm that the dog’s neck measurement falls inside the collar’s adjustable range. A collar that starts at 14 inches on a 13-inch neck forces you to cinch it to the very last hole, leaving no room for comfort or growth.
For chain collars, add 4 inches instead of 2. For open-end belt-style collars, round the neck measurement down to the nearest even number before ordering.
Where the Collar Actually Belongs
The collar should sit high on the neck, just below the ears and the jawbone. That placement lets the collar rest on the narrower part of the neck where it cannot slide off. A collar sitting mid-neck or down near the shoulders is positioned wrong and will not stay put. High placement also keeps pressure off the trachea, which makes walks more comfortable and reduces coughing.
The two-finger test is non-negotiable. After fastening the collar, slide two fingers between the collar and the dog’s neck. If you cannot get two fingers in, the collar is too tight. If you can fit three or more fingers, the collar is too loose and the dog can slip out. One finger is the bare minimum for non-adjustable collars, but two fingers is the standard for everyday wear.
Reading the Sizing Charts Correctly
Different brands use different measurements. Some list neck range in inches. Others suggest a weight range. Always go by the neck measurement over the weight suggestion — a lean 60-pound dog and a stocky 60-pound dog need different collar lengths. The table below shows how four common brands handle sizing so you can see the pattern.
| Brand / Model | Size | Neck Range (Inches) |
|---|---|---|
| The Black Dog | XS | 6–12 |
| The Black Dog | S | 9–15 |
| The Black Dog | M | 12–18 |
| The Black Dog | L | 15–21 |
| Wild One | Extra Small | 7–10 |
| Wild One | Small | 8–12 |
| Wild One | Medium | 12–15 |
| Wild One | Large | 15–18 |
| Fi Series 3+ | Small | 10.5–13 |
| Fi Series 3+ | Medium | 12.5–16.5 |
| Fi Series 3+ | Large | 15.5–22 |
If a full-grown dog falls exactly between two sizes, choose the smaller size for a snugger fit. For a growing puppy, choose the larger size so the collar lasts longer. When you are picking out a collar for a young dog that still has growing to do, the sizing rules shift — our roundup of collars built for a growing labrador puppy lays out which designs handle the weight gain best.
How to Adjust a Standard Nylon Collar
Most nylon collars use a tri-glide slider. To shorten the collar, move the tri-glide away from the buckle by looping the extra nylon through and pulling tight on the buckle end. To lengthen it, slide the tri-glide toward the buckle and pull on the buckle to remove the slack. The goal is a collar that sits high on the neck with exactly two fingers of space underneath.
After adjustment, the collar should stay in place without sliding when you tug it gently. A well-fitted collar will not spin around the dog’s neck and will not ride up toward the ears.
One final check: the collar must be snug enough that it cannot be pulled over the dog’s head. If you can slip it off with a light pull, tighten it one more hole. A collar that comes off easily is a lost collar waiting to happen.
For the official sizing guide from Coastal Pet Products, the same two-finger and high-placement rules apply across all their collar styles including martingale and chain models.
Common Mistakes That Ruin a Good Fit
Most fit problems come from ignoring the collar’s position. A collar placed low on the neck near the shoulders lets a dog back out of it in seconds. A collar that is loose enough to slide over the dog’s head is an invitation to escape.
Over-tightening is just as dangerous. A collar that presses against the throat can cause coughing, gagging, or restricted breathing. Check for redness, hair loss, or irritation around the neck every few days, especially when breaking in a new collar.
Ignoring growth is another frequent miss. A puppy that gets a collar fitted for its 8-week-old neck will outgrow that fit in a month. Check the fit weekly for the first year and adjust as needed. Puppy owners often find that buying a size up earlier saves them the hassle of replacing collars every few weeks.
Special Collar Types: Their Own Rules
Chain collars need 4 extra inches added to the neck measurement, not the standard 2 inches. The extra length gives the chain room to loosen and tighten properly during use. The dog’s weight also helps determine the correct chain gauge.
Prong collars require the same 2-inch addition as standard collars, but the wire gauge is chosen by the dog’s weight. Many prong collars allow you to add or remove links to adjust the working length.
Open-end belt-style collars need a different rounding approach: measure the neck and round down to the nearest even number. A 19-inch neck calls for an 18- to 21-inch collar. This keeps the buckle holes from landing awkwardly off-center.
Final Fit Checklist: Confirm Before You Walk Out the Door
| Check | Pass / Fail |
|---|---|
| Collar sits high on the neck, just below the ears | ☐ |
| Two fingers slide easily between collar and neck | ☐ |
| Collar cannot slip over the dog’s head | ☐ |
| Collar does not spin or slide when tugged | ☐ |
| No coughing or gagging when the dog pulls | ☐ |
| Measured neck falls inside the collar’s adjustable range | ☐ |
| No loose threads or detachable parts that could be swallowed | ☐ |
Run through these checks every time you adjust the collar or buy a new one. A correct fit stays comfortable for the dog and keeps the collar where it belongs — on the dog, not on the ground.
FAQs
What happens if a collar is too loose?
A loose collar allows a dog to slip out of it during walks or in the yard. It can also slide around the neck and create a choking hazard if the collar catches on a fence or branch. The two-finger test prevents this.
Can I use a collar measurement from a harness?
No. A harness sits around the chest and rib cage, which is wider than the neck. Using a harness measurement for a collar will give you a collar that is too large and will fit poorly at the correct high-neck position.
How often should I check a puppy’s collar fit?
Check the fit every week during the first year of growth. Puppies can outgrow a collar size in two to three weeks. A collar that fits in the morning can feel tight by the end of the month.
What do I do if the collar causes hair loss or redness?
Remove the collar immediately and let the area rest for a few days. Clean the collar thoroughly and check for rough edges or trapped debris. If the irritation returns, try a wider collar that distributes pressure better, or switch to a softer material like neoprene.
Is the two-finger rule the same for every breed?
Yes, the two-finger rule applies to all breeds, but very small breeds like Chihuahuas may need a one-finger check because two adult fingers could be too thick. For tiny dogs, use one finger as the comfort gap instead.
References & Sources
- Coastal Pet Products. “Sizing Guide” Official source for chain-collar 4-inch rule, prong-collar sizing, and two-finger placement standard.
- Kindred Heart Vet. “How to Properly Choose and Put on a Dog Collar” Covers high-neck placement and safety checks for collar fit.
- GoTags. “Sizing Guides” Explains adjustable range matching and open-end collar rounding rules.
- The Black Dog. “Dog Size Chart” Full brand sizing table for XS through L collar ranges.
- Wild One. “Collar Size Guide” Size chart with strap widths for XS through L collars.