How to take the three measurements
- Chest girth. Around the widest part of the ribcage, just behind the front legs. This is the one that decides harness size, and it is the one people skip. Snug, with room for two fingers underneath.
- Neck girth. Where the collar actually sits, which is lower than you think — not right up under the jaw. Two fingers should slide flat underneath when it is fastened.
- Back length. From the base of the neck, where a collar sits, straight back to the base of the tail. This sets coat length, bed size and crate size.
- Height at the shoulder, if you want a crate size. Floor to the top of the shoulder blade, with them standing.
Do it while they are standing, not lying down, and write the numbers in your phone. You will use them again every time you buy anything, and they change slowly.
Why S, M and L mean nothing
There is no standard behind them. One maker's large is another's medium, and the same brand often sizes its coats and its harnesses differently. The letters on this page are the common bands, not a rule — they are there so you know roughly where to look. The measurement in inches is the only thing that transfers between brands, which is why every good size chart is published in inches and centimetres.
What a good fit looks like
- Collar: two fingers slide flat underneath. If a third fits, it comes off over the ears the first time something interesting crosses the road.
- Harness: two fingers under the chest strap, and nothing rubbing in the armpit. Lift a front leg forward — the strap should not dig into the crease.
- Crate: long enough to lie flat on their side with legs out, tall enough to stand without ducking, and no bigger. A crate the size of a room stops being a den. For a puppy, buy adult size and use the divider.
- Bed: measure the dog, then add 10 inches. Most dogs sleep stretched out more than curled, and the bed people buy is one size too small because the curled-up shape is what they picture.
Two breed shapes that break the chart
Deep-chested dogs — greyhounds, whippets, dobermans — have a neck girth close to their head width, so ordinary collars slip straight off. That is what a martingale is for, and it is a safety item rather than a style choice.
Flat-faced and thick-necked breeds — pugs, French bulldogs, bulldogs — often measure a size up on the neck and a size down on the back. Harness over collar for these, always: pressure on the throat is the last thing an airway that is already narrow needs.