Guide

How to Measure Your Dog for a Collar or Harness

Breed and weight are poor predictors of fit. This guide shows where to place the tape for neck and chest measurements, how to use the two-finger check, and how to read a manufacturer size chart without guessing.

Last reviewed August 10, 2026. This guide is general information, not veterinary advice.

Why breed and weight are not enough

Two dogs of the same breed and weight can need different sizes, because chest depth, neck thickness, and coat volume vary considerably between individuals. Manufacturer size charts are built around measurements, and the breed names some brands print alongside them are only a rough hint.

Measuring takes a couple of minutes and removes most of the guesswork, particularly for harnesses, where a poor fit can slip, chafe, or restrict shoulder movement.

What you need

A soft tape measure: the kind used for sewing; it follows the body contour accurately.
Or a piece of string: wrap it, mark the overlap point, then lay it flat against a rigid ruler.
A standing dog: measure with the dog standing squarely on all four feet, not sitting or lying down.
A second person: helpful for a wriggly dog, and it keeps the tape at a consistent tension.

Measuring the neck for a collar

For dogs with thick or seasonal coats, remember the measurement will change after grooming. An adjustable collar handles this far better than a fixed-length one.

Stand the dog squarely and find the base of the neck, where a collar naturally sits above the shoulders.
Wrap the tape around that point, keeping it level rather than angled.
Draw the tape snug against the coat without compressing it, and read the measurement.
Apply the two-finger check: you should be able to slide two fingers flat between the tape and the neck.

Measuring the chest girth for a harness

Chest girth is the measurement most harness charts are built around. Find the widest part of the ribcage, usually a short distance behind the front legs, and wrap the tape all the way around the body at that point, keeping it level on both sides.

Some harnesses also ask for a neck or shoulder measurement, taken lower on the neck than a collar measurement, closer to where the chest strap will sit. Follow whichever measurements the specific manufacturer lists rather than assuming they are interchangeable between brands.

The fit check once it is on

Two fingers: you should be able to slide two fingers flat under any strap; more than that and the dog can back out of it.
Shoulder movement: watch the dog walk; straps should not cut across the front of the shoulder joint and restrict the stride.
Armpit clearance: the chest strap should sit clear of the armpit, which is the most common place for rubbing.
Skin and coat: check for redness or hair loss after the first few walks, which usually indicates rubbing or a strap too tight.
Recheck regularly: growing puppies, weight change, and seasonal coat changes all alter the fit.

What to do when the dog falls between sizes

Check whether the adjustment range of each size overlaps your measurement, and prefer the size where your measurement sits in the middle of the range rather than at either extreme. A measurement at the very end of a range leaves no room for coat change, weight change, or growth.

For a growing puppy, buying the adult size early rarely works: a harness that is too large is easy to escape from. It is usually safer to buy for the current size and replace it as the dog grows.

Common questions

Where exactly do I measure a dog's chest?

Around the widest part of the ribcage, typically just behind the front legs, with the tape level all the way around and the dog standing squarely. This is the measurement most harness size charts are based on.

How tight should a collar or harness be?

Snug enough that the dog cannot back out of it, loose enough that you can slide two fingers flat underneath any strap. If you can fit a whole hand under it, it is too loose; if you struggle to get two fingers in, it is too tight.

Should I size up for a puppy?

Generally no. An oversized harness or collar is easy for a puppy to slip out of, which is a safety problem. Buy for the current measurement, choose an adjustable design, and re-measure regularly during growth.

Can I use one brand's size chart for another brand?

No. Sizing is not standardised, and a medium in one range can differ substantially from a medium in another. Always compare your measurements against the chart for the specific product you are buying.