The first thing that you simply have to do is make a list of the entire selection of alliances that you are going to be walking away and if possible, try to get a rough idea of how big each of the items actually is. Although this can be a sufficient time consuming thing to do, this is one of the most accurate ways to make sure that the unit you are going to rent will be adequate for all of your possessions.
This can also have other positive effects because you might see all of your many belongings and realize that you probably do not need some of them, which can then lead you into getting rid of the item for good rather than waste money on storing the item with the rest of your things.
You then need to phone around and speak to a few storage companies, because these are the people that have all of the experience when it comes to choosing to correct unit for you and your possessions. Because this is their job, they will be able to offer you some sound advice and get to the bottom of exactly what you need, which can make choosing the right unit much easier.
You can also go online and find a self storage company that has some sort of interactive size guide or video, which can help to make it clear and simple and explain exactly what you need in visual terms rather than lots of text and numbers. Some of the latest interactive size guides are quite funky and can offer a really good idea about how big a unit you will really need.
You may also decide that one of the best things you can do is to actually go and visit the site and see the different options for yourself. Going back to the visual kind of things, it can often be easier to work out sizes when you know how much stuff you need to store and then see the space available to you.
Most self storage companies are also quite flexible, so if you make it clear that you are not 100% sure about the size you need from the outside, then they might allow you to increase the size you need on the day of arrival, but always make sure you check this first because it will often be down to availability.