What size checked suitcase should I buy?

A 25-inch medium checked bag suits one- to two-week trips and is easier to keep under airline weight limits, while a 28- or 29-inch large is better for longer trips or families sharing a bag. Remember that a fully packed 29-inch softside can exceed the 50-pound limit, so the lighter the empty bag, the more you can pack before incurring overweight fees.