There are several factors to consider when determining the luggage size to buy. Firstly, think about the duration of your trip. For example, a smaller suitcase or carry-on might suffice if you're going on a weekend getaway.
For longer trips, consider purchasing a larger checked bag. Secondly, consider the weight restrictions of your airline. Many airlines have size and weight restrictions for luggage, so make sure to check their website before making a purchase. Lastly, think about your personal packing habits.
If you tend to overpack, opt for a slightly larger bag to avoid cramming everything in and potentially damaging your belongings.