How to Choose the Right Dog Collar Size: Complete Measurement Guide

A collar that’s too loose slips off. A collar that’s too tight causes chafing, discomfort, and can restrict breathing. Getting the right fit takes two minutes of measuring and knowing which common mistakes to avoid.

How to Measure Your Dog’s Neck

What You Need

A soft measuring tape (the flexible kind used for sewing)
If you don’t have one: a piece of string or a strip of fabric, plus a ruler

Step-by-Step

Find the right spot. Measure where the collar will sit - the middle of the neck, roughly halfway between the ears and the shoulders. This is not the base of the neck near the chest.
Wrap the tape snugly. Pull the measuring tape around the neck with enough tension that it doesn’t sag but doesn’t compress the fur or skin. Think “firm but not tight.”
Read the measurement. Note the number where the tape meets itself. This is your dog’s actual neck circumference.
Add 2 inches. The collar should be adjustable to this measurement plus 2 inches. This allows you to fit two fingers between the collar and the neck - the universal fit test.

The Two-Finger Test

After putting the collar on, slide two fingers (flat, side by side) between the collar and your dog’s neck:

Can’t fit two fingers: Too tight. Loosen or size up.
Two fingers fit snugly: Correct fit.
Three or more fingers fit: Too loose. Tighten or size down.

Size Chart by Breed

Breed Examples	Neck Size	Recommended Width	Collar Size
Chihuahua, Yorkie, Pomeranian	6-10”	3/8”-1/2”	XS
Shih Tzu, Maltese, Toy Poodle	8-12”	3/8”-1/2”	XS-S
French Bulldog, Pug, Beagle (small)	12-16”	1/2”-3/4”	S-M
Cocker Spaniel, Border Collie, Bulldog	14-18”	3/4”-1”	M
Labrador, Golden Retriever, GSD	16-24”	1”-1.5”	L
Rottweiler, Doberman	18-26”	1”-1.5”	L-XL
Great Dane, Mastiff, St. Bernard	22-34”	1.5”-2”	XL-XXL

These are guidelines, not rules. Individual dogs vary widely. A muscular Bulldog might have a thicker neck than a lanky Lab. Always measure rather than guessing by breed.

Common Measurement Mistakes

Measuring Too Low

The most common error. Many people measure at the base of the neck (near the shoulders) instead of where the collar actually sits. The base can be 2-3 inches larger, resulting in a collar that rides up toward the ears unintentionally.

Measuring Over Thick Fur

Fluffy breeds (Samoyeds, Huskies, Pomeranians) need the tape pressed into the coat slightly - you’re measuring the neck, not the fur. If you measure over the fur, you’ll get a number that’s 1-2 inches too large.

Not Accounting for Growth

Puppies grow quickly. Buy an adjustable collar in the current size with room to let out as they grow. Check the fit weekly - a collar that fit last week can be tight this week during rapid growth phases.

Buying the “They’ll Grow Into It” Size

A collar that’s too large is useless for leash control and can slip over the dog’s head. Puppies typically go through 2-3 collar sizes before reaching adult dimensions. Budget for this rather than buying one oversized collar.

Width Matters Too

Collar width affects both comfort and pressure distribution:

Dog Weight	Recommended Width	Why
Under 10 lbs	3/8”-1/2”	Narrow collars sit between jaw and shoulders without bunching
10-25 lbs	1/2”-3/4”	Balance of comfort and strength
25-60 lbs	3/4”-1”	Standard width for most medium dogs
60-100 lbs	1”-1.5”	Wider distributes pressure for strong dogs
100+ lbs	1.5”-2”	Maximum width for giant breeds

Wide collars on small dogs bunch up and restrict head movement. Narrow collars on large dogs concentrate pulling force on a thin line, which is uncomfortable and can cause tracheal irritation.

Special Sizing Situations

Brachycephalic Breeds (Flat-Faced)

Pugs, French Bulldogs, Boston Terriers, and Bulldogs have necks that are often as wide as or wider than their heads. Flat collars can slip over the head easily. Consider a martingale collar or a harness for leash walking instead.

Sighthounds (Greyhounds, Whippets)

The opposite problem: heads wider than necks. Flat collars slip off easily when the dog pulls backward. Martingale collars are nearly mandatory for these breeds - they tighten gently to prevent escape without choking.

Puppies

Measure weekly during growth phases (8-16 weeks, then monthly until adult size). Buy the cheapest adjustable collar that fits now - don’t invest in premium collars until your dog reaches adult size.

Dogs Between Sizes

If your dog’s measurement falls between two sizes, size up. It’s easier to tighten an adjustable collar than to stretch one that’s too small. A slightly loose collar adjusted properly is better than a maximum-tightened collar with no room to adjust.

When to Recheck Fit

Weekly for puppies under 6 months
Monthly for puppies 6-12 months
Every 3 months for adults
After significant weight change (diet change, pregnancy, illness recovery)
After grooming - haircuts can change neck diameter by half an inch or more
Seasonally - some dogs develop thicker necks in winter (double-coated breeds)

For collar recommendations once you know your size, see our best dog collars guide and collar types comparison.

Frequently Asked Questions

Can I use a human measuring tape?

The rigid metal kind? It works but curves awkwardly around a dog’s neck. A soft sewing tape is ideal. Alternatively, wrap a piece of string around the neck, mark where it meets, and measure the string with a ruler.

Should the collar be tighter for training?

No. The same two-finger rule applies whether the collar is for daily wear or training. A training collar that’s too tight causes discomfort and interferes with the training. Martingale collars self-adjust during corrections - you don’t need to tighten them preemptively.

My dog has a very thick neck but small head. What collar works?

Martingale collars are designed for exactly this situation (common in Bulldogs and Pit Bulls). The collar loosens around the thick neck for comfort but tightens around the narrower point behind the head to prevent escape.

How do I measure for a harness instead of a collar?

Harnesses typically require two measurements: chest girth (the widest part of the ribcage, just behind the front legs) and neck circumference. Some harnesses also require a weight measurement. Check the specific harness manufacturer’s sizing guide, as harness sizing varies more between brands than collar sizing does.