How to choose a storage unit size
Choose a storage unit size by estimating the volume of your belongings in cubic feet, dividing by about 75 per cent of the unit's gross volume to allow for realistic packing, and taking the next size up if the result fills more than 85 per cent. Floor area alone will mislead you, because you store by volume, not by footprint.
- 5 steps
- No calculator required
- The 85% rule
Step 1: List what actually goes in
Write down every item that will be stored. The two rooms people forget are the garage and the closets, and between them they routinely account for a third of a household's volume.
Anything you are selling, donating or leaving behind does not belong on the list. This is also the cheapest moment in the whole process to decide that the treadmill is not coming.
Step 2: Convert the list to cubic feet
Storage is bought by volume. Each item has a packed cubic-foot value — the space it occupies as loaded, including what its shape wastes. Common anchors:
| Item | Packed volume |
|---|---|
| Three-cushion sofa | 50 cu ft |
| Queen bed set | 60 cu ft |
| Double dresser | 40 cu ft |
| Refrigerator | 50 cu ft |
| Dining table | 30 cu ft |
| Medium box | 3 cu ft |
| Wardrobe box | 11 cu ft |
Full values for 110+ items in our furniture dimension dataset.
Add them up. That total is the only number that matters from here — the volume guide covers the arithmetic in more detail.
Step 3: Apply a packing factor
A unit's advertised volume is not what you can fill. Nobody stacks perfectly, sofas do not tessellate, and the top eighteen inches usually go unused.
| Packing density | Fraction of gross volume | What it looks like |
|---|---|---|
| Loose | 70% | Nothing stacked above head height, fragile items, room to move things around. |
| Moderate | 85% | Stacked to around 7 ft with furniture placed sensibly. The default. |
| Tight | 93% | Stacked to the ceiling, uniform boxes, disassembled furniture. Needs planning. |
Use 85% unless you have a specific reason not to. Divide your total by 0.85 to get the gross unit volume you need, then find the smallest unit that clears it in the size chart.
Step 4: Decide whether you need an aisle
This is the step most guides skip and the one that most often decides the answer. A unit packed to the door is cheaper; a unit you can walk into is usable.
| Unit | Usable, no aisle | Usable with a 15% aisle | Difference |
|---|---|---|---|
| 5×5 | 170 cu ft | 145 cu ft | −25 cu ft |
| 5×10 | 340 cu ft | 289 cu ft | −51 cu ft |
| 5×15 | 510 cu ft | 434 cu ft | −76 cu ft |
| 10×10 | 680 cu ft | 578 cu ft | −102 cu ft |
| 10×15 | 1,020 cu ft | 867 cu ft | −153 cu ft |
| 10×20 | 1,360 cu ft | 1,156 cu ft | −204 cu ft |
If the rental will last more than a few months, or if anything seasonal is going in, assume you need the aisle.
Step 5: Check the door, not just the unit
Sizes and door widths for every unit are listed on storage unit sizes, and packing planner sequences the load once you have them. Volume decides the size; the door decides whether your furniture gets in. Roll-up doors are typically 8 ft wide on a 10 ft unit and 4 to 5 ft on a 5 ft unit, and both are narrower than the unit behind them.
Measure your longest and widest single item — usually a sofa, a mattress or a dining table — and compare it with the door opening and the corridor turn. A 5 ft wide unit will not accept a 7 ft sofa in any orientation. What to measure and how.
The 90 per cent rule
Worked through the five steps and want to check it? The storage unit size calculator runs exactly this method over your item list and returns the minimum, the recommended and the comfortable size with a fill rate for each.
Related questions
What size storage unit do I need?
Divide your inventory volume in cubic feet by 0.85, then choose the smallest unit above that figure. As an anchor, a studio is about 278 cu ft, a two-bedroom about 630 cu ft, and a three-bedroom house about 1,168 cu ft.
Should I round up or down when unsure?
Up. The cost difference between adjacent sizes is typically $20–$60 a month; the cost of a second rental is a second move of everything you already carried once.
Do I need to include boxes in the estimate?
Yes. Boxes are commonly 20–30% of a household's stored volume and are the single most under-counted category. Use the box calculator if you have not packed yet.