I'll be honest—when I first started keeping dogs after years of focusing on aquariums, I made the rookie mistake of eyeballing collar sizing. Figured if it looked about right, it'd work fine. Ended up with a collar that my Shiba Inu could slip out of during walks, which taught me real quick that how to measure dog for collar sizing isn't something you guess at. Just like how I learned you can't eyeball water parameters in a reef tank, proper collar measurement requires actual numbers and a methodical approach.
In this guide, I'm walking you through exactly how to measure your dog for a collar using techniques I've refined over the years—some learned from trainers, others from my own trial-and-error. You'll learn the proper measurement technique, how to account for different coat types and growth stages, and how to translate those measurements into the right collar size. This is beginner-friendly stuff that takes maybe five minutes once you know what you're doing, but getting it right the first time saves you the hassle (and expense) of returns or, worse, a collar that compromises your dog's safety.
What You'll Need
- Soft fabric measuring tape (the kind used for sewing—not a metal retractable tape measure, which can pinch skin and give inaccurate readings)
- Your dog (obviously, but they should be calm and standing in a natural position)
- Two fingers (for the fit test—your index and middle fingers work best)
- Pen and paper or phone (to record the measurement immediately so you don't forget it)
- The dog's current collar (optional, but helpful for comparison if they're already wearing one)
- Treats (for dogs who won't sit still—positive reinforcement makes this whole process smoother)
Step 1: Position Your Dog and Locate the Measurement Point
Getting your dog into the right position matters more than you'd think. I learned this the hard way when I measured my friend's Great Dane while he was sitting, then wondered why the collar I bought was way too tight when he stood up—his neck circumference changed by nearly two inches between positions.
Have your dog stand in a natural, relaxed stance on a flat surface. They shouldn't be sitting, lying down, or stretching their neck forward. If you've got a squirmy puppy or an excitable adult dog, this is where those treats come in handy. I usually have someone else feed small treats to keep the dog's attention forward while I work around the neck area.
The correct measurement point is the widest part of the neck, which for most dogs sits right where the neck meets the shoulders—basically where a collar naturally rests when your dog is moving around. For dogs with thick ruffs like Collies or Pomeranians, you'll need to feel through the coat to find where the neck actually is, not just measure the fluff. What I've found works well is running my hand down from behind the ears to feel where the neck starts to widen into the shoulder area. That's your measurement zone.
For brachycephalic breeds (dogs with pushed-in faces like Bulldogs, Pugs, and French Bulldogs), pay special attention here because their neck circumference can be surprisingly close to their head circumference, which affects how collars fit and whether they can back out of them.
Step 2: Wrap the Measuring Tape Around the Neck
Now take your soft fabric measuring tape and wrap it around your dog's neck at that widest point you just identified. The tape should sit flat against the fur or skin, following the contour of the neck without twisting or bunching up. I hold one end of the tape at the top of the neck with my left hand, then bring the rest of the tape around with my right hand until the numbers meet back at the starting point.
Here's where different coat types require different approaches. For short-coated breeds like Beagles, Pit Bulls, or Dobermans, this is straightforward—the tape sits right against the skin and you can see what you're doing. For double-coated or long-haired breeds like Golden Retrievers, Huskies, or Shih Tzus, you need to make a choice about whether you're measuring over the coat or compressing it down to the skin level.
In my experience, measuring at a medium tension works best—not tight enough to compress the coat completely down to skin, but not so loose that you're measuring air and fluff. You want the tape snug enough that it's making contact with the coat layer that will sit under the collar during normal wear. Think of it like getting a measurement that represents the dog's "working diameter" rather than either extreme.
If your dog has a thick ruff or mane around the neck area, I've found it helps to smooth the coat down in the direction it naturally lays, then measure over that. Don't try to flatten it completely or you'll end up with a collar that's too tight when the coat poofs back up.
Step 3: Check the Tape Position and Read the Measurement
Before you read off that number, double-check that the measuring tape hasn't shifted during the process. Dogs move, you move, and that tape can easily slide up toward the head or down toward the shoulders without you noticing. I usually do a quick visual check from the side and from above to make sure the tape is sitting level all the way around and hasn't twisted anywhere.
The tape should be lying flat and horizontal around the neck, not angled upward toward the ears or downward toward the chest. If you're working with a dog who has a very thick coat, run your fingers under the tape at several points around the neck to confirm it's at a consistent depth in the fur.
Once you're confident the position is right, read the measurement where the tape overlaps at the starting point. Most fabric measuring tapes show both inches and centimeters—I typically record both just to cover my bases, since different collar manufacturers use different units. For reference, if you see something like 14 inches or 35.5 centimeters for a medium-sized dog, that's the kind of range that makes sense. Puppies might be anywhere from 8-14 inches depending on breed and age, while giant breeds like Mastiffs or Saint Bernards can easily measure 24-30 inches.
Write this number down immediately. I used to think I'd remember it, then I'd get distracted by the dog or another task, and by the time I sat down to order a collar I'd have no idea if it was 15 or 16 inches. Save yourself that second measurement and just record it right away.
Step 4: Add Space for the Two-Finger Rule
Here's the part that trips up a lot of first-time dog owners: the measurement you just took is not the collar size you should order. That number represents the circumference of your dog's neck, but a properly fitted collar needs breathing room. The standard guideline in dog training and veterinary circles is the two-finger rule—you should be able to slide two fingers (placed flat, not stacked) between the collar and your dog's neck comfortably.
To translate this into a collar size, you typically add 2-3 inches to your neck measurement. So if your dog's neck measures 14 inches, you'd be looking at collars in the 16-17 inch range. The exact amount depends partly on your dog's coat thickness and partly on the collar style you're planning to use, which is something I cover more in Understanding Dog Collar Types: Materials, Styles, and Uses Explained.
For very short-coated dogs with thin necks (like Whippets, Italian Greyhounds, or Min Pins), I lean toward adding just 2 inches since there's less coat to account for and these breeds can sometimes slip collars if there's too much slack. For thick-coated breeds, adding a full 3 inches makes more sense because the coat compresses under the collar during wear, and you don't want it getting tight as the coat expands after baths or during seasonal coat changes.
Puppies are a special case here, which ties into why best dog collars for puppies focuses so much on adjustability. For dogs under six months old, I actually add closer to 3-4 inches to allow for rapid growth, but only if the collar has enough adjustment range to still fit snugly now. You'll be sizing up soon anyway, so don't invest in expensive custom-fit options for this stage.
Step 5: Verify the Fit With the Two-Finger Test
If your dog is already wearing a collar, or once you receive the new collar you've ordered, you need to physically test the fit rather than just trusting the numbers. I can't count how many times I've ordered something based on measurements that looked perfect on paper, only to find the actual fit was off once the product arrived—collar construction varies between manufacturers, and what one brand calls a "16-inch collar" might fit differently than another brand's version.
Put the collar on your dog at a length that corresponds to the measurement you calculated (your dog's neck circumference plus 2-3 inches). Then slide your index and middle fingers, held flat and together, between the collar and the side or front of your dog's neck. You should be able to slide them in without forcing it, but there shouldn't be so much room that you could fit your whole hand in there or stack three or four fingers.
When I do this test, I check multiple points around the collar, not just one spot. Sometimes a collar sits unevenly due to coat thickness variations or the way the dog's neck tapers, and what feels right at the front might be too loose at the back. Rotate around the neck and verify the two-finger fit is consistent.
If you can't get two fingers in, the collar is too tight and needs to be loosened or sized up. If you can fit three or four fingers easily, it's too loose and your dog could potentially slip out of it or get a paw caught trying to scratch at it. I had a neighbor whose Aussie got a front leg stuck through a too-loose collar while scratching, and it was terrifying for everyone involved until they got it untangled.
Step 6: Account for Special Sizing Considerations
Some dogs require adjustments to the standard measuring approach I've outlined. Sighthounds (Greyhounds, Whippets, Salukis, Borzois) have necks that are nearly as wide as their heads, which means they can back out of standard flat collars even when sized correctly. For these breeds, I've learned you need to either measure for a martingale-style collar that prevents slipping, or if you're committed to a flat collar, you might need to go a half-inch tighter than the two-finger rule would suggest—though this is something to discuss with your vet or a trainer who knows the breed, since you're balancing security against comfort.
Brachycephalic breeds like Bulldogs, Pugs, and Boston Terriers often have necks that are very close in size to their heads, and they can also have respiratory considerations that make collar tightness a more serious issue. For these guys, I err on the side of a slightly looser fit and make sure I'm using a harness for walks rather than putting any pulling pressure on the neck.
Very young puppies (8-16 weeks) are growing so fast that a collar that fits perfectly today might be uncomfortably tight in two weeks. When I measure puppies in this age range, I add the full 3-4 inches as I mentioned earlier, but I also check the fit every few days by doing the two-finger test. Growth spurts can catch you off guard, and you don't want a collar that was fine on Monday to be digging into their neck by Friday.
Senior dogs sometimes develop conditions like hypothyroidism or Cushing's disease that cause weight and muscle distribution changes, including around the neck. If you've got an older dog who's been wearing the same collar size for years, it's worth re-measuring periodically to make sure the fit hasn't changed. I learned this when a friend's elderly Lab ended up with neck irritation because his collar had become too tight as his muscle mass decreased but his coat thickness increased with age.
Step 7: Cross-Reference With Collar Sizing Charts
Once you've got your measurement plus the added space for the two-finger rule, the last step is matching that number to the manufacturer's sizing chart for the specific collar you're buying. This is where things can get a bit frustrating because there's no universal standard—one company's "medium" might be another company's "large," and adjustable collars have different useful ranges even within the same nominal size category.
Most quality collar manufacturers provide a size chart that lists a neck circumference range for each size rather than a single number. For example, a medium might be listed as fitting necks 14-18 inches. Your calculated size (let's say 16 inches for a dog with a 14-inch neck) should fall somewhere in the middle of that range, not at either extreme. If you're at the very bottom of a size range, you might not have enough collar length to achieve a secure fit, and if you're at the very top, you'll have excessive collar strap flopping around that your dog could step on or that could catch on things.
I always check the adjustment range listed for adjustable collars. Some cheap collars advertise a wide size range but only have maybe 3-4 inches of actual adjustment, which means they don't really fit most of that advertised range well. Better collars have 6-8 inches of adjustment within a size category, giving you room to fine-tune the fit and accommodate coat changes or minor weight fluctuations.
If you're torn between two sizes, my general rule is to size up for puppies and thick-coated breeds, size down for thin-coated breeds with slender necks, and go with the larger size if you're ordering a collar style you haven't used before and want the flexibility. You can always make a collar shorter by adjusting it, but you can't add length to one that's too small. That said, when looking at the full range of options in something like top dog collars: complete guide to choosing the right collar, you'll find that the best approach is often to choose a brand known for accurate sizing in your dog's specific size range rather than trying to make a poorly-sized collar work.
Pro Tips & Common Mistakes
Don't measure over a collar your dog is already wearing. I've seen people do this thinking it'll save time, but you're just adding the thickness of the existing collar to your measurement, which throws everything off. Remove any collar or bandana first, then measure the actual neck.
Coat condition matters more than you'd think. If you measure right after a bath when the coat is wet and compressed, or right after a grooming when the coat is blown out and fluffy, you'll get different numbers than the dog's everyday coat state. I try to measure when the coat is in its normal, dry, unstyled condition—basically how it looks most of the time.
One mistake I made early on was not accounting for seasonal coat changes in double-coated breeds. My friend's Husky wears a collar that fits perfectly in summer, but when that undercoat comes in for winter, the same collar gets noticeably tighter. For these dogs, you might need to remeasure twice a year and adjust accordingly, or choose a collar with enough adjustment range to accommodate both states.
Using a metal tape measure or a retractable ruler instead of soft fabric tape is harder than it needs to be. The rigid edge can poke your dog and make them squirmy, and it's difficult to wrap it smoothly around a curved surface like a neck. Fabric measuring tapes (like the [SINGER ProSeries Tape Measure] or any basic sewing tape) cost about a dollar and make this whole process ten times easier.
For dogs who absolutely won't stand still for measuring, I've found that measuring while they're eating works surprisingly well. Put their food bowl down, wait for them to settle into eating, then quickly and gently wrap the tape around while they're distracted. Just don't pull on the tape or you'll spook them mid-meal, which is a good way to create negative associations with the process.
Frequently Asked Questions
How tight should a dog collar be?
A properly fitted dog collar should follow the two-finger rule: you should be able to comfortably slide two fingers (held flat, not stacked) between the collar and your dog's neck at any point around the circumference. The collar should be snug enough that your dog can't back out of it or get a paw caught underneath when scratching, but loose enough that it's not restricting breathing, causing coughing, or creating pressure points on the neck. For most dogs, this translates to ordering a collar size that's 2-3 inches larger than the actual neck circumference measurement, though thick-coated breeds may need the full 3-inch addition while thin-coated sighthounds might need slightly less.
What size collar does a puppy need?
Puppy collar sizing depends entirely on breed, age, and expected adult size, but the measurement process is the same as for adult dogs: measure the neck circumference at the widest point and add 3-4 inches rather than the standard 2-3 inches to allow for rapid growth. An 8-week-old Labrador puppy might measure around 10 inches and need a collar that adjusts from 12-16 inches, while a same-age Chihuahua might measure 6 inches and need a 9-12 inch collar. The most important factor isn't the initial size but choosing a collar with a wide adjustment range (at least 4-6 inches within a size category) since puppies can outgrow a fixed-size collar in as little as two weeks during growth spurts, and you should recheck the fit with the two-finger test every few days until they reach skeletal maturity around 12-18 months depending on breed.
Can I use a string to measure my dog's neck if I don't have a measuring tape?
Yes, you can use a non-stretchy string or ribbon as a substitute measuring tool—just wrap it around your dog's neck following the same technique as you would with a fabric tape measure, mark or hold where the string overlaps at the starting point, then lay the string flat against a ruler or metal tape measure to read the length. The key is using something that doesn't stretch (cotton string, dental floss, or a ribbon works fine; elastic cord or yarn doesn't) and making sure you mark the overlap point clearly before removing it from the dog, since it's easy to lose your place once the string is off the neck. This method works in a pinch, though a fabric measuring tape is more convenient and accurate since you can read the measurement directly without the transfer step.
How often should I check my dog's collar size?
For adult dogs with stable weight, checking the collar fit every 3-4 months with the two-finger test is usually sufficient, though you should recheck sooner if your dog gains or loses weight, gets a dramatic haircut, or if you notice any signs of discomfort like coughing when pulling on leash or scratching excessively at the collar area. Puppies need weekly or even twice-weekly fit checks from 8 weeks to 6 months old due to rapid growth, then monthly checks from 6-12 months as growth slows, and quarterly checks after that. Senior dogs benefit from more frequent checks (every 4-6 weeks) since age-related conditions can cause shifts in weight distribution and muscle mass that affect how a collar fits, and double-coated breeds may need seasonal adjustments when their undercoat grows in or sheds out, as coat density changes can affect the effective neck circumference by a half-inch or more.
Summary
Learning how to measure dog for collar sizing properly takes maybe five minutes but saves you from ordering the wrong size, dealing with returns, or worse—ending up with a collar that's uncomfortable or unsafe for your dog. The process is straightforward: position your dog standing naturally, wrap a soft fabric measuring tape around the widest part of the neck, add 2-3 inches to that measurement to account for the two-finger rule, then cross-reference with the manufacturer's sizing chart. Pay attention to special considerations like coat type, age, and breed characteristics, and always verify the final fit with the actual two-finger test once the collar is on your dog.
The techniques I've shared here come from both my own experiences measuring dogs of different sizes and coat types, and from conversations with trainers and vet techs who've seen what happens when collars don't fit right. Just like how I learned in fishkeeping that water parameters need to be measured, not guessed, collar sizing requires actual numbers and a systematic approach. Take the extra few minutes to do it correctly, and you'll end up with a collar that keeps your dog safe and comfortable whether they're a 5-pound Chihuahua or a 150-pound Mastiff.
