What Size Storage Unit Do You Actually Need?
You are standing in the office of a storage facility and someone has asked what size you need. You say "about a two-bedroom's worth?" — because that is the unit the question seems to want — and thirty seconds later you are renting a 10 by 10 and hoping.
It is a strange purchase. You are buying a volume, sight unseen, to hold a set of belongings you have never measured, and the bill arrives every month for as long as you get it wrong. One size too big and you pay for air, indefinitely. One size too small and you spend a Saturday discovering it, then pay to move up.
The answer is not the calculator on a facility's website, which was built by the people selling the space. It is twenty minutes of counting what you actually have.
The sizes you will be offered
Facilities vary, but the ladder is close to standard, and it is worth knowing before anyone quotes you:
5 by 5 — a large closet. Seasonal gear, a few boxes, a bicycle if you are careful.
5 by 10 — a walk-in closet. A studio's worth: a mattress on its side, a small sofa, boxes to the ceiling.
10 by 10 — half a garage, and the most commonly rented size. A one to two bedroom household, packed properly.
10 by 15 — a full one-car garage. Two to three bedrooms, or one bedroom plus a workshop's worth of equipment.
10 by 20 — a full garage. Three to four bedrooms, or a car.
10 by 30 — rare, and usually more than a household needs.
Two adjustments to make immediately. Ceiling height is commonly around eight feet and sometimes considerably more, which matters more than the floor area — see below. And a drive-up unit and an interior unit of the same nominal size are not the same purchase: the interior one costs you a corridor, and possibly a lift, on every single visit.
Why the room-count estimate is wrong
Every size guide translates units into bedrooms, and the translation is where the error enters. A two-bedroom household ranges enormously. Two bedrooms with a minimalist and a futon is a 5 by 10. Two bedrooms with a piano, a home gym and eleven years of accumulation is a 10 by 15, and the person quoting you cannot see the difference.
Worse, the estimate is being made about the wrong set. You are not storing your household. You are storing the part of it that is not coming with you — which might be a quarter of it or nearly all of it, and only you know which.
So do not answer in bedrooms. Answer in boxes and large items, which are countable.
Count what you actually have
This is the whole method, and it takes an afternoon at most.
Walk the rooms and list the large items that are going into storage. Sofa, mattress, wardrobe, dining table, desk, appliances, bicycles, the exercise machine. Anything that will not go in a box.
Estimate the boxes. Count what you have already packed and scale up — if a third of the house is packed into 20 boxes, you are heading for about 60. If nothing is packed, count shelves and drawers instead: a full bookshelf is roughly four to six boxes, a chest of drawers roughly four.
Photograph as you go. One picture per large item and one per stack. This becomes the record you will want later, and it costs nothing to make now, while everything is still visible.
Add the awkward ones separately. A mattress, a rolled rug, a ladder, skis, a Christmas tree. None of these stack, and none of them fit an estimate that thinks in boxes. Name them individually.
Now translate. A standard moving box is roughly one and a half cubic feet; a large one closer to four or five. Sixty medium boxes is somewhere around 120 cubic feet, which stacked six feet high occupies about 20 square feet of floor — a fifth of a 10 by 10. It is almost always the large items, not the boxes, that decide the size.
The aisle nobody budgets for
Here is the most common sizing mistake, and it is not about volume at all.
If you will ever need to retrieve one item before you empty the unit, you cannot pack it wall to wall. You need a walkway down the middle, and stacks you can reach from it. That aisle costs you roughly a fifth to a quarter of the floor.
So the question is not only "how much do I have." It is "am I storing this, or am I visiting it." A unit you will not open until the day you empty it can be packed solid, and you should size it accordingly. A unit you will visit monthly needs to be one size up from the pure volume answer, and the extra rent is buying you the ability to use it at all.
Most people answer "I won't need to go in" in the office and are back within six weeks.
Height is the cheapest space you are already paying for
You are renting a volume and almost everyone uses two thirds of it. The floor is fully occupied by month two and there is three feet of air above everything.
The practical version: heavy boxes on the bottom, uniform box sizes so the stacks are stable, and a cheap shelving unit along one wall — which turns the top third of the unit into usable space and makes the aisle work. Furniture on end where it is safe to stand it. Mattresses upright against a wall rather than flat, where they otherwise consume an entire footprint for one item.
Getting the height right is often the difference between one size and the next, which is a difference you pay every month.
Size up or size down when you land between
If your count falls between two sizes, the tiebreakers, in order:
Will you retrieve from it? If yes, size up. The aisle is not optional, and a unit you cannot walk into stops being usable.
How long will it be? For three months, size down and pack tight. For two years, size up — you will add to it, everybody does.
Is a second small unit an option? Sometimes two small units cost less than one large, and sometimes the reverse. Ask, because facilities price by what is empty rather than by arithmetic.
What is the transfer policy? Many facilities will move you to a different unit mid-lease. If yours will, guessing costs less and you can start smaller.
After you sign, the part that saves the second drive
Whatever size you land on, the record is what makes the unit usable. A unit you cannot see into is one you drive to in order to find out what is in it, and that drive is the real cost of getting this wrong.
Make the list as it goes in, not later. This is where an app does something a note cannot. Photograph an open box and the AI identifies the contents into the record, so the list gets made while you are loading rather than in a second pass. Every box gets a permanent three-word name and you can print a QR label for it, so a scan shows what is inside without opening it. A location can belong to more than one household, which is what makes a unit shared with family readable by both of you. And the inventory is searchable, which is the entire point: "camping gear" from your sofa, rather than a Saturday.
If the unit is already full and you never made the list, our guide to inventorying a storage unit without emptying it is the two-visit version. And if this is part of a move, the move timeline covers what happens on either side of the unit.
One last honest point. The best answer to "what size do I need" is sometimes "smaller than you are about to rent, because a third of this is not worth storing." The count in step one is where that becomes obvious, and it is the only part of this exercise that saves you money every month rather than once.
Cratify is free to try.