The size of the storage unit you should get depends on the amount and type of items you plan to store. It's important to choose a unit that is large enough to accommodate all your belongings without being too cramped. You can start by making an inventory of the items you want to store and estimating their total volume. This will give you an idea of the size of unit you need. Additionally, you may want to consider any future storage needs you may have, as it might be more cost-effective to rent a slightly larger unit now rather than having to upgrade later.