A donut bed is measured across the outside. That is the industry convention, and it is the number on the box, the listing, and our own product page. But it is not the number your dog sleeps in.
The ring takes up room
A donut bed is a raised ring around a sunken center. The ring is the point — it is what a dog presses their back into, what makes the bed feel enclosed. But the ring runs the full circumference, and it has thickness. On a bed sold as 100 cm, part of that 100 cm is ring.
The space inside, where the dog actually lies, is smaller. And on most listings nobody mentions it at all.
Why we publish the outer measurement
We give the outer diameter because it is the one figure that stays the same. The space inside changes with the dog: a heavier dog compresses the ring and gains room, a lighter one sits higher on the fill and loses it. A single inner number would be right for one dog and wrong for the next.
So we give you the measurement you can check with a tape the day the bed arrives, and we describe what happens inside the ring rather than putting a figure on it that only holds for some dogs.
So how do you choose
Think about the dog curled, not stretched. A donut bed is for dogs who tuck — they turn, they press their spine into the ring, they settle. A dog who sleeps flat on their side will find the ring in the way, and will be happier on a rectangular bed.
For the Halo, the 100 cm outer diameter suits medium breeds of roughly 8 to 18 kg — Corgi, Beagle, Shiba Inu, Cocker Spaniel, French Bulldog. Dogs at the top of that range will fill the center. Dogs at the bottom will have room to spare.
If your dog is near an edge of that range, or if they are a sprawler, email us their weight and breed. We would rather tell you a bed will not fit than sell you one that goes back.