Measure your dog’s neck where the collar sits and add two fingers of room; that number, not weight, picks the right size.
A collar that’s too tight chafes and strains, while one that’s too loose slips right over the head. The reliable way around both is a simple neck measurement — figure out the inches, compare them to a sizing chart, and you’ve got the right fit. Below is the measuring method, the size ranges to expect, and the mistakes that throw people off.
How To Measure Your Dog’s Neck For A Collar
Grab a soft tape measure and wrap it around the neck at the spot where the collar actually sits — usually the widest part of the neck, just above the shoulders. You want the tape snug but not pressing into the fur, and you should be able to slide two fingers between the tape and the neck. That gap is the breathing room a dog needs to be comfortable all day.
No tape measure handy? Use the old-collar method. Lay the current collar flat and measure from the buckle’s pin to the hole you normally use — don’t include the buckle itself in that number. That gives you the exact size that already fits, which you can then compare against a sizing chart.
If the neck measurement falls between two sizes on a chart, size up rather than down. A slightly loose collar is safer than one that’s tight.
Understanding Sizing Chart Ranges
Charts group sizes by neck circumference in inches, and the bands differ by brand. PetSmart’s chart, for example, runs from 6–8 inches for the smallest sizes up to 16–26 inches for the largest. Coastal Pet’s guide lists bands like 8–12 inches, 10–16 inches, 19–23 inches, and 30–43 inches depending on the product line.
The takeaway: there’s no universal standard. A size M from one maker can fall at 13–20 inches, while another brand’s M might start at a completely different number. Always check the specific chart for the collar you’re buying.
Table: Comparing Common Sizing Bands
| Retailer Guide | Size Bands (Neck Inches) |
|---|---|
| PetSmart | 6–8, 8–10, 10–14, 14–18, 16–26 |
| Coastal Pet | 8–12, 10–16, 19–23, 20–28, 30–43 |
| dogIDs | XS 8–12, S 10–15, M 13–20, L 16–26 |
Notice how much overlap exists between adjacent sizes. That’s why the measurement matters more than the letter on the tag.
Common Sizing Mistakes To Avoid
The biggest error is picking a collar by breed or weight. Chihuahuas and Whippets both weigh around 15 pounds but have completely different neck shapes — the fit comes from the tape measure, not the scale. Charts may list breed examples for reference, but treat those as hints, not rules.
- Don’t include the buckle when measuring a flat collar; measure only the strap from the buckle pin to the hole you use.
- Don’t measure too loose. The tape should sit snugly against the fur; loose measuring leads to an oversized collar that slips.
- Watch the width, not just the length. Two collars in the same size can have different strap widths, which changes how they sit on a short or long neck.
- Check metric vs. imperial. Many charts list centimeters alongside inches — make sure you’re reading the right column.
When in doubt, size up and adjust. Most collars have a couple of inches of adjustment range, and a collar that’s slightly roomy beats one that digs in. If you’re shopping for a growing puppy, remember that necks change fast — plan to re-measure every few weeks and check the best dog collars for puppies to find adjustable options that grow with them.
References & Sources
- PetSmart. “Sizing Charts.” Provides official neck-size ranges for collar products.
- Coastal Pet. “Sizing Guide.” Lists product-specific size bands in inches and centimeters.
- dogIDs. “Sizing Guides.” Shows XS-to-L neck circumference ranges for its collars.