This large Snoozy pet carrier was just what I was looking for.  I transported  my six month old Sheltie, who weighed about 15 lbs. and stood 13.5 inches at the shoulders.  She was comfortable and it was perfect solution for  her in-cabin air flight.  Although it is the larger size, it fit under the seat ahead of me after I removed the middle support bar.  The optional backpack method was convenient for going up and down the escalators, and while hauling my travel bags.  The roll around was perfect for moving quickly through the airport. My Sheltie was protected, snug, and stress free.