My pet is an 11 pound Rat Terrier and I purchased the carrier rated for 25 lbs. She still seemed a bit cramped in it. But she is a good girl and gave it a go so off we went to the street fair. If you are wheeling this carrier with your pet, cracked and uneven sidewalks are not your friend so you are better off using the back pack feature.  Also, crowds can be a problem as some folks do not look where they are walking and tripped over her in the carrier. 

None of these problems are the fault of the carrier which is well made and a good deal for the price.