Short answer
Measure what you're storing, add room for an aisle and air gaps, then pick the smallest standard size that fits. Common sizes run from 5x5 to 10x20, and 10x10 is the most popular. In a climate-controlled unit, leave space around items so the conditioned air can reach them.
The right size is the smallest one that holds your things with a little room to spare. Because climate-controlled space costs more per square foot, guessing too large is an expensive mistake.
The standard sizes
Most facilities offer the same set of sizes. The Self Storage Association says typical units range from 5x5 to 10x20, with the average about 100 square feet, the size of a 10x10.
| Unit | Floor area | Good starting point for |
|---|---|---|
| 5x5 | 25 sq ft | Boxes, files, a few small items |
| 5x10 | 50 sq ft | Boxes plus a few pieces of furniture |
| 10x10 | 100 sq ft | Furniture and boxes from a small home |
| 10x15 | 150 sq ft | A larger household’s furniture |
| 10x20 | 200 sq ft | The contents of a larger home |
Floor area is only half the story. Ceiling height varies by building, so ask. Stacking boxes higher adds a lot of space without paying for more floor.
The most popular size
The 10x10 is the industry’s workhorse. The SSA’s 2020 demand study found that 10x10 “continues to be the most common unit size,” and that 10x10 and 10x20 units are growing in popularity. Businesses tend to rent 10x30 or larger.
How to size it yourself
- List the big pieces. Measure sofas, beds, dressers, tables and appliances.
- Count the boxes. Measure one of each box size you use, and work out how many fit in a stack under the ceiling.
- Plan your stacks. Heavy boxes on the bottom, furniture upright where safe, mattresses on edge.
- Add an aisle. You’ll want to reach items at the back without unpacking the front.
- Add air gaps. In a climate-controlled unit, keep items a few inches from the walls so conditioned air can circulate.
That last point matters more than people expect. NDSU Extension advises storing things away from the outside wall to allow air circulation, and making sure everything is thoroughly dry before it goes in. Packing a unit wall to wall works against the climate control you’re paying for.
When to size up
- You’ll need regular access, so you need a wider aisle.
- You’re storing long items, like a sofa, rugs or a piano.
- You expect to add more items later.
When to size down
- You can stack boxes to the ceiling.
- You can take apart bed frames and table legs.
- Some of your items are durable enough for a cheaper standard unit, so you can split the load.
Splitting is worth considering. Keep the furniture, photos and electronics in a smaller climate-controlled unit, and put tools and plastic bins in a standard unit or garage.
To check what sizes are available, call a few verified facilities near you. In a big market like New York City or Brooklyn, ask whether the size you want is open now or only on a waitlist.