This depends on the amount of stuff you need to store, and how accessible you need it to be. If you access items throughout the unit, then a larger unit will allow you to organize the space so that everything is accessible. If you are simply stacking and leaving items, a smaller unit can hold a lot of items. We have a size chart in the office that shows estimated items that fit in the units. Also, feel free to stop by the facility to examine a unit in person to get a better idea of what size you will need.