What size carrier do I need for a large (15-20 lb) cat?

Reviewers across r/CatAdvice repeatedly flag that carriers marketed for 'large cats up to 20 lbs' are often too cramped in practice — a recurring complaint about soft-sided options like the Gapzer when used with cats over 18 lbs. For genuinely large cats, look at hard-sided XL options (the SportPet XL is rated to 35 lbs) and measure your cat's length from nose to base of tail before buying.