Measuring
Use your maker's own sizing guide and measure the way it says. Sizes are not the same from one maker to another.
Ring first
Most discomfort comes from the ring. Too tight and it pinches or restricts blood flow; too loose and it rubs or slips. If you are between sizes, start with the larger.
The gap and the length
Some cages set the gap between ring and shell with a spacer. A shell that is too short presses when you are soft; too long and it moves and chafes.
Give a new cage a few days of short wear before a longer lock.
What the survey heard about fit
In Chastity Report 2026 (71 submissions), the same nominal ring size felt different from one maker to another, and advice on going smaller or larger conflicted. There is no universal sizing shortcut.
Two or three cages is normal
You do not need to get this right on the first try. Most people go through two or three cages.
Signs a size is wrong
This is shared experience, not medical advice. Pinching, rubbing that breaks the skin, a ring that leaves marks that do not fade, numbness, a change of colour or swelling all mean the size is wrong.
The last three mean take it off now, and the When to take the cage off guide says what to do next.
Ring first, then the cage. If it pinches, it is the wrong size, not the wrong person.
Erik