If you're considering renting a 10x20 storage unit, you might wonder how many boxes you can fit inside. While the answer may vary depending on the size and contents of your boxes, you can generally expect to fit about 200 medium-sized boxes in a 10x20 storage unit. Of course, if you're planning to store larger items, such as furniture or appliances, you'll need to adjust your estimate accordingly. But if you're simply looking for a place to store extra boxes of belongings, a 10x20 unit should give you plenty of space. And if you're still not sure, most storage facilities offer free estimates, so you can always give them a call and ask for help in choosing the right unit for your needs.