How to Measure Your Dog for a Collar? | The Right Fit Every Time

A collar that’s too tight can choke or rub a raw spot, while one that’s too loose lets a nervous dog back out and bolt. Getting the right measurement takes two minutes with a fabric tape, a piece of string, or even the dog’s current collar. Here’s exactly how to do all three, what happens when different collar types change the rules, and the one measurement mistake that makes the whole effort useless.

Why the Right Collar Fit Matters More Than You Think

An ill-fitting collar isn’t just a comfort issue. A collar that restricts breathing can cause coughing or stress, while one that slips off is a safety risk during walks. The two-finger test (or one-finger for martingale-style training collars) is the universal check because it balances security against comfort. Every method below builds toward that single test.

The Three Ways to Measure a Dog’s Neck Size

Method 1: Using a Fabric Tape Measure or String

This is the most accurate method and works for every collar type. You’ll need a soft fabric tape measure or a non-stretchy string and a ruler.

• Position the tape where the collar sits. For flat and buckle collars, wrap it around the mid-neck area. For prong or martingale collars, measure right behind the ears — the placement is different because these collars sit higher on the neck per Herm Sprenger’s sizing guide.
• Snug but not tight. The tape should follow the natural curve of the neck, not dig in. Fluffy or thick coats don’t count — measure at the skin and fur base, not the bulk of the fur. BayDog specifically warns that measuring over thick winter fur can add two inches and ruin the fit.
• Check the clearance. You must be able to slide one finger (for a closer fit on martingale or training collars) or two fingers (for standard flat collars) between the tape and the neck. PetSmart and Coastal Pet both recommend two fingers for everyday buckle collars.
• If you used string, mark the overlap and lay it flat against a rigid ruler to get the inch measurement.

Method 2: Measuring Your Dog’s Current Collar

If the current collar fits well, this is the fastest route — but only if you measure the right spot.

• Remove the collar and lay it flat. Stretch it out fully so there are no twists in the material.
• Measure from the center of the buckle to the sizing hole currently in use. This is the number that equals your dog’s actual neck size. Tactipup and DogIDs both emphasize this step because the buckle itself takes up space.
• Do not measure end-to-end. That mistake adds one to two inches to the reading. If your dog is between sizes, that extra inch pushes you into the wrong range, and the collar will be loose.

Method 3: Phone Charger Cable Hack

No tape measure or string handy? A phone charger cable works as a stand-in. Hold one end between your fingers, wrap it gently around the neck at the thickest area, and pull snug enough that two fingers fit between the cable and neck. Mark where the cable meets the end, then measure that length with any tape measure you have. Tactipup confirms this works as well as a fabric tape.

Standard Collar Size Chart

The table below shows the general size ranges most brands follow. Your dog’s measured neck circumference should fall entirely within the listed range for that size.

Brand sizes vary — Wild One’s L tops out at 18 inches while PetSmart’s L goes to 26, so always check the specific brand’s chart before ordering. For adjustable collars, choose a range where your dog’s measurement falls near the middle so you have room to go tighter or looser as needed.

Special Collar Types Change the Measurement Rules

Chain and Slip Collars

These need extra length to function because the chain tightens around the neck. The standard rule from Coastal Pet and Herm Sprenger is to add 3 to 4 inches to the neck circumference for a slip or chain collar. A dog with an 18-inch neck would need at least a 22-inch chain. The wire gauge of the chain depends on the dog’s weight — heavier dogs need thicker links.

Prong and Martingale Collars

Measure right behind the ears rather than at mid-neck, because these collars sit higher. For prong collars with an assembly chain, add about 2 inches to the behind-the-ears measurement. Never measure a prong collar at mid-neck — the fit will be wrong, and the collar won’t sit in its intended position.

Open-End and Belt-Style Collars

If your dog’s neck measures an odd number (say, 19 inches), round down to the nearest even number and order a collar whose range includes that even size (18–21 inches). GoTags clarifies that collars need to fit within the stated range, not at its edge.

Three Mistakes That Ruin a Collar Fit (and How to Avoid Them)

• Measuring end-to-end on the old collar. Always measure from buckle center to the used hole.
• Including the fur. The measurement goes around the neck skin, not the coat fluff. A Collie or Husky with a thick mane needs a collar sized to the fur base.
• Guessing by weight. Breed weight ranges vary by inches. Tape the neck; don’t guess the size.

Once you have the correct measurement, you’re ready to shop. For a curated list of durable, well-reviewed options that match common neck sizes, check our top picks for the best dog collars.

How to Check the Fit After You Buy

The two-finger test is the final gate. Slide two fingers under the collar at the side of the neck. If the fingers slide in easily but there’s light resistance, the fit is correct. If the collar slides freely over the dog’s head, it’s too loose. If you can’t fit one finger, it’s too tight. For growing puppies, opt for the larger size if the measurement sits between two sizes. For full-grown dogs, pick the smaller of the two to avoid extra material that can catch on furniture.

Final Collar Fit Checklist

Before you call the job done, run this quick check:

• The collar sits at the correct height on the neck (mid-neck for standard, behind the ears for training collars).
• You can fit two fingers between the collar and the neck (one finger for martingale collars).
• The collar doesn’t rotate freely around the neck or slip over the widest part of the head.
• The buckle or clasp is not digging into the dog’s throat or causing coughing.
• For chain collars: the chain is at least 3 inches longer than the neck circumference.