The short answer for a Selkirk Rex
Most adult Selkirk Rex cats fit a medium-large carrier about 20 to 22 inches long, 13 inches wide, and 13 to 14 inches tall. That is a step up from a standard medium carrier, and the reason is build, not just weight: a Selkirk Rex is a medium-to-large cat with heavy bones, a broad chest, and a thick, curly coat that adds real bulk. Inside the carrier, she should be able to stand with her ears clear of the roof, turn around without her coat compressing hard against the walls, and lie stretched out with her legs extended. If she has to hunch or keep her legs tucked to fit, the carrier is too small, whatever the label says.
Why the curly coat changes the measurement
A Selkirk Rex's coat is the complicating factor in every measurement. The curls stand away from the body, so a tape measure laid over the coat can overstate her frame, while a carrier chosen by weight alone can understate how much room those curls occupy once she settles. Measure her body length from nose to tail base with the tape resting lightly on the coat, then add a few inches for turning room. Measure height from the floor to the top of her head while she stands, and add a small margin for the pad inside. A carrier that is long but narrow will still feel tight to this breed.
Strength, doors, and airflow for a solid cat
A Selkirk Rex is a substantial cat, so carrier strength matters as much as size. Choose a rigid, hard-sided carrier with sturdy latches and a handle rated for a heavier load, and test it yourself by lifting it with your cat inside before the first real trip. A wide front door helps, because guiding a broad, curly cat through a narrow opening can tangle the coat and start the trip with a struggle; a top opening is a useful second option for a relaxed cat. Ventilation deserves attention too: a thick curly coat traps warmth, so look for airflow on at least two sides and avoid wrapping the carrier in heavy blankets on a warm day.
Settling a calm Selkirk Rex into the carrier
Selkirk Rex cats are generally patient and people-oriented, which makes carrier training straightforward if it starts early. Leave the carrier open in a room she already uses, with a familiar blanket inside, and let her wander in and out without any pressure. A few treats placed just inside the door will usually do the rest, and many Selkirk Rex cats will nap in an open carrier within a week. Before travel, brush out any loose curls gently so the coat is not matted by the journey, and check that no stray curls are caught in the door latch when you close it.
Common sizing mistakes for this breed
The most common mistake is buying a carrier that fits a Selkirk Rex's length but not her width, followed by choosing a soft-sided bag whose sides bow inward under her weight. Another mistake is sizing from a kitten's curly fluff, which exaggerates length while hiding the solid frame underneath, then never upgrading as she matures. If your Selkirk Rex is a larger male, lean toward the top of the size range or step up to a large carrier rather than squeezing her into a medium-large shell. Extra room costs nothing in comfort for a cat who can brace her feet, while a tight fit makes every bump a problem. In KinsLe, Family Sharing keeps the Selkirk Rex's carrier dimensions, latch check, and coat notes in one shared profile, so anyone travelling with her uses the same sturdy setup she already trusts.