There are about 6 different sizes of luggage if you want to get really specific. There are personal item-size luggage (about 17" long), international carry-on (about 21" tall), domestic-carry on (about 22" tall), small checked luggage (23-24" tall), medium checked luggage (25-27" tall), and large checked luggage (28-32" tall). These sizes are based on airline regulations since most people use their luggage for flying. Airlines only accept luggage of certain sizes depending on how much you've paid for your ticket and where you're going. People like to have luggage in a few different sizes so they can adapt to however they are traveling.