Why Your Unit Mix Drives the Whole Pro Forma

A 5×5 and a 10×20 are not the same dollars per foot — they're not even close. Get the mix wrong in your model and you'll misprice the entire deal.

Ask someone new to storage what their building will rent for and they'll give you one number: "about a dollar a foot." That single blended figure is where a lot of storage pro formas quietly go wrong — because storage doesn't rent at one rate. It rents at a dozen rates, and which ones dominate your building is set by your unit mix.

Small units win on dollars per foot — by a lot

The counterintuitive rule that runs all of storage economics: smaller units rent for far more per square foot than larger ones. A small unit might command $1.40 per square foot per month while a large one fetches $0.70 — the small unit earns double the rent per foot of space it occupies.

Illustrative rates to show the gradient; real numbers come from your market's comps.

Why does the small unit win? Two reasons. A renter storing a few boxes isn't price-sensitive to a $35 unit the way they would be to a $140 one — the absolute dollar is small, so the per-foot premium hides. And demand for small units is deep and sticky: people store "a little stuff" for years. Large units turn over faster and compete more directly with cheaper alternatives (a garage, a friend's barn).

The mix is your blended rate

Because each size rents differently, your building's overall rate is just a weighted average of the mix. Tilt toward small units and your blended $/sf climbs; load up on big drive-up units and it falls. This is why "about a dollar a foot" is not an input — it's an output of how many of each size you build.

Which means underwriting with one average rate across the whole building can throw your revenue off by 20–30% depending on how the mix actually lands. On a deal where the development spread is a hundred basis points wide, a 20% revenue error isn't a rounding issue — it flips the verdict.

Designing the mix: demand, not just dollars

Higher $/sf doesn't mean "build nothing but 5×5s." A few guardrails:

• Match the mix to local demand, which a feasibility study or submarket data informs. Over-build small units in a market that wants vehicle and household storage and you'll have high asking rates and empty units — a great blended rate on paper, terrible economic occupancy in reality.
• Mind the lease-up. Small units fill faster and turn over more; large units lease slower but stick. The mix shapes your absorption curve, not just your rate.
• Climate vs. non-climate is part of the mix. Climate-controlled units rent at a premium over drive-up of the same size — but cost more to build and operate. The right split is a return question, not a default.
• Leave room for the high-demand sizes. 10×10 and 10×15 are the workhorses of household demand; a mix with none of them ignores where a lot of the market actually is.

Don't forget the income that rides on units

Two revenue lines scale with your unit count, not your square footage, which is another reason the mix matters. Tenant insurance or protection plans attach per occupied unit — at strong penetration they add on the order of 8–10% of total revenue, at high margin. And admin and late fees are per-tenant. A mix heavy on small units means more tenants per square foot, which means more of this per-unit income. Underwrite those lines off your unit count once the mix is set.