The useful question isn't how many square feet it is — it's how many rentable units come out of it, and what kind. Here's what the common footprints actually give you.
Most people start a self-storage project with a number in their head — a building size, or a piece of land. The useful question isn't how many square feet it is. It's how many rentable units come out of it, and what kind.
This page walks through the common footprints, what each typically yields, and what makes one right for your site.
A caveat worth reading first: the unit counts below are typical layouts, not quotes. Drive-aisle width, door placement, corridor design and unit mix all change the count. Use them to understand the shape of the decision, then run your numbers or ask us for a real layout.
Building width sets your unit depth. A 30-foot-wide building gives two rows of 15-foot-deep units back to back. A 40-foot-wide building gives two rows of 20-foot units. Width is the decision that constrains everything after it.
Building length sets your unit count. Divide by unit width — usually 10 feet — and multiply by two for back-to-back rows.
That's the whole arithmetic. What makes it a real decision is unit mix and demand: a market that wants small units and a market that wants boat parking need different buildings on the same piece of land.
Single-loaded: one row of 15-foot-deep units, typically 10 units at 10×15.
The smallest footprint that makes commercial sense. Suits an infill lot, an expansion phase, or a market you're testing before committing. Lower absolute return, but also the lowest entry cost and the easiest to add to later.
Same single-loaded design, longer run: typically 13 units at 10×15.
Good fit for a narrow or awkwardly shaped parcel where depth is constrained but length isn't. Three more units than the 15×100 for proportionally less cost, since the fixed costs are already covered.
Double-loaded: two rows of 15-foot-deep units, typically 20 units at 10×15.
The 10×15 is a workhorse unit — a household's worth of furniture, a contractor's tools and materials. Twenty of them is a real facility rather than a trial.
Same design, longer: typically 24 units at 10×15.
The size the search data suggests people are actively pricing. The extra 20 feet adds four units against a fixed foundation and roof system — better cost per unit than the 30×100.
Two rows of 20-foot-deep units, 20 units at 10×20.
The extra depth changes who rents from you. A 10×20 takes a car, a boat trailer, or a full household. Same unit count as the 30×100, meaningfully higher rent per unit. One of ROI's four packaged specials.
Mixed-unit layout rather than uniform. Mixing sizes captures a wider tenant base and cuts vacancy risk — you're not dependent on one segment of the market showing up. Packaged special.
Purpose-built for boat storage. 10×10 doors with extra height clearance, sized for small to medium boats. If you have property near water, this is a different and often less competitive market than household storage.
10 oversized 15×50 bays with 12×14 doors. Built for Class A motorhomes and fifth wheels. The highest rent per unit of anything on this list, and the tenants stay longest — an RV owner isn't moving out next month.
| Footprint | Sq ft | Typical units | Best for |
|---|---|---|---|
| 15 × 100 | 1,500 | 10 @ 10×15 | Infill lots, phase one |
| 15 × 130 | 1,950 | 13 @ 10×15 | Narrow or deep-constrained parcels |
| 30 × 100 | 3,000 | 20 @ 10×15 | First real facility |
| 30 × 120 | 3,600 | 24 @ 10×15 | Better cost per unit than 30×100 |
| 40 × 100 | 4,000 | 20 @ 10×20 | Higher rent per unit, vehicle-capable |
| 30 × 150 | 4,500 | mixed | Wider tenant base, lower vacancy risk |
| 35 × 120 × 12 | 4,200 | boat bays | Waterfront and lake markets |
| 50 × 150 × 16 | 7,500 | 10 @ 15×50 | RV and motorhome, longest tenancies |
Typical layouts, not quotes — drive aisles, door placement and unit mix all change the count.
The fixed costs — site work, foundation, permits, mobilisation — don't scale with size. That's the argument for building larger.
The argument against is that an oversized facility in a thin market is vacant square footage you're paying to heat, insure and maintain. Lease-up rate matters more than unit count, and a full 20-unit building beats a half-empty 40-unit one on every measure that matters.
If you don't know your market's absorption rate, that's the number to find before you pick a footprint. Our feasibility guide covers how to think about it.
The building footprint is not the site requirement, and this is where projects get stuck at the planning stage. A 30×100 building does not fit on a 30×100 piece of land.
Drive aisles are the biggest addition. Drive-up units need enough width for a vehicle to pull in, stop, and back out without a three-point turn. Typical is 24 to 30 feet — closer to 30 where you have drive-up units on both sides of the aisle.
Turning space at the ends. A truck with a trailer needs room to come around the end of a building. Undersized end space is the most common complaint from tenants who otherwise like the facility.
Setbacks vary by jurisdiction and are the one number you cannot estimate from a rule of thumb. Check them before you fall in love with a parcel.
A working rule of thumb: for a single building with drive-up access, plan on usable site area of roughly two to two and a half times the building footprint. A 3,000 sq ft building wants something in the range of 6,000 to 7,500 sq ft of usable ground once aisles and maneuvering are accounted for.
That ratio improves as you add buildings — a second row shares the aisle between them rather than needing its own.
If you're evaluating a parcel rather than a building, work backwards: take the usable area after setbacks, divide by roughly 2.25, and that's the approximate building footprint the site supports. Then come back to the table above.
Aisle widths and the site-area ratio above are general industry planning practice, not ROI engineering specifications. Your jurisdiction, site shape and access plan govern.
Square footage is the smallest part of the answer. What actually moves the number:
Run your dimensions through the calculator for an all-in cost range, or browse the pre-priced packages if one matches what you had in mind.
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