Storage Unit Size Calculator
Add up what you are storing and see which unit actually holds it — gaps and aisle included.
What are you storing?
Recommended unit
5 × 10
- Your belongings
- 165 ft³
- Usable share of a unit
- 56% (packing + aisle)
- Gross space needed
- 293 ft³
- Floor area needed
- 37 sq ft
- Unit floor area
- 50 sq ft — Walk-in closet
- Headroom
- 36% spare capacity
Unit sizes are nominal — a 10 × 10 is often slightly under. Measure doorways and check the clear height if you are storing anything tall.
Every size against your load
| Unit | Floor | Usable volume | Verdict |
|---|---|---|---|
| 5 × 5 (Closet) | 25 sq ft | 113 ft³ | Short by 53 ft³ |
| 5 × 10 (Walk-in closet) | 50 sq ft | 225 ft³ | Fits |
| 10 × 10 (Half a garage) | 100 sq ft | 450 ft³ | Fits |
| 10 × 15 (Single garage) | 150 sq ft | 675 ft³ | Fits |
| 10 × 20 (Standard garage) | 200 sq ft | 900 ft³ | Fits |
| 10 × 30 (Double garage) | 300 sq ft | 1,350 ft³ | Fits |
Throwing things out instead of storing them? Size a dumpster →
How this is calculated
belongings = Σ (item count × packed ft³ each)
usable share = packing efficiency × (1 − aisle%)
gross needed = belongings / usable share
floor needed = gross needed / 8 ft clear height
recommended = smallest unit where
floor × 8 ft × usable share ≥ belongingsThe two allowances stack because they remove different things: packing efficiency covers the gaps between awkward objects once stacked, and the aisle removes floor area you never fill at all. Turning the aisle off is the single biggest change you can make — it moves most inventories down a full unit size, and it is the right call whenever the unit gets packed once and emptied once.
What each unit typically holds
| Unit | Gross volume | Usable at 75% | Typical contents |
|---|---|---|---|
| 5 × 5 | 200 ft³ | 150 ft³ | Closet |
| 5 × 10 | 400 ft³ | 300 ft³ | Walk-in closet |
| 10 × 10 | 800 ft³ | 600 ft³ | Half a garage |
| 10 × 15 | 1200 ft³ | 900 ft³ | Single garage |
| 10 × 20 | 1600 ft³ | 1,200 ft³ | Standard garage |
| 10 × 30 | 2400 ft³ | 1,800 ft³ | Double garage |
Gross volume assumes the standard eight foot clear height, and the usable column applies the same 75% packing efficiency the calculator defaults to, with no aisle. Facilities quote the floor area only, so the height is what decides whether a unit is generous or tight.
Frequently asked questions
What size storage unit do I need?
A 5×10 holds roughly the contents of a one bedroom apartment, a 10×10 a two bedroom, and a 10×20 a three to four bedroom house with appliances. Those rules assume you stack to the ceiling and pack tightly, so if you plan to walk in and retrieve things you should size up one step.
How high can I stack in a storage unit?
Most units have an eight foot clear height, and facilities generally allow stacking to within a foot of the ceiling for sprinkler clearance. In practice few people fill the top third safely, which is why this calculator applies a packing efficiency well below 100% rather than assuming a perfect cube of belongings.
Do I need an access aisle?
If you will visit the unit and pull individual items out, yes, and it costs roughly a quarter of the floor space. Pure long-term storage packed once and emptied once needs no aisle, which is the single biggest lever on what size you can get away with.
Is climate control worth it?
It matters for wood furniture, electronics, instruments, photographs, artwork and anything leather, particularly in humid or freezing climates. For garden tools, plastic bins and general household clutter it usually is not worth the premium, which commonly runs 25 to 50% above a standard unit.
How many boxes fit in a 5×5 unit?
A 5×5 gives about 200 cubic feet of gross space, and at realistic packing efficiency roughly 150 usable. That is on the order of 50 medium boxes stacked to the ceiling with nothing else in the unit, or around 30 boxes plus a mattress set and a few small pieces.
Should I round up a size?
Usually yes if the estimate lands within about 15% of a unit's capacity, because inventories grow between planning and moving day and a too-small unit forces a second rental at a worse rate. The exception is long-term storage of a fixed, already-boxed inventory, where the tighter unit saves real money every month.
Results are planning estimates. Item volumes are typical packed sizes and vary widely with how well things disassemble and nest. Facilities differ on clear height, stacking rules and what may be stored — confirm with yours before booking.