Renting a storage unit? You will want to make sure that your possessions will fit in it before you load up and move your belongings. It would be sad to start putting your items into the unit only to discover there isn't enough room and you have to take some of it back home.
So before renting, make a list of what furniture and boxes you have and their sizes and shapes and then compare it to the space available. Remember the space is vertical as well as deep and wide. There are a lot of items that you can fit into the storage unit, you just have to plan well.
Put the heavy things on the bottom. Then lighter things on top of them.
Put the items you will need again soon in the front and the items you won't be needing for a while at the back.