How to Determine the Right Unit Mix for a New Self Storage Facility

Unit mix is the proportion of units you offer in each size, and it’s one of the earliest decisions when starting a self storage business. It’s also one of the most expensive to get wrong, because the layout, structure, doors and circulation are all built around it. We’d suggest starting with demand, not the floor plan. Base your mix on who you’ll serve, what competitors offer locally and what the site allows. Then design in enough flexibility to adjust once real customers arrive.

Why unit mix matters

• Revenue: Smaller units generally earn more per square foot, while larger units earn less per square foot but often attract longer stays and business customers. Neither is automatically better, and the balance matters.
• Occupancy: A mix that’s out of step with local demand leaves you full in one size and empty in another.
• Cost of change: Moving partitions, doors and services later means spend, disruption and lost income.

Step 1: Understand who you’re serving

Different customers need different spaces:

• Households: moving, decluttering, renovating or downsizing
• Students: short-term, smaller units
• Small businesses and trade: stock, tools, documents and equipment
• E-commerce sellers: frequent access and often mid-sized units

Look at the catchment. Areas with lots of flats and limited home storage tend to lean towards smaller units, while areas with a strong trade or small-business base may need more mid-sized and larger space.

Step 2: Audit local competition

Find out what sizes competitors offer, what they charge per square foot and which units are sold out or discounted. Look for gaps too, such as climate-controlled space, ground-floor access or drive-up units. Be careful with “sold out” signals, though. A full size band may mean under-supply, or it may mean it’s underpriced.

Step 3: Read the building and the site

The physical building will shape what’s possible:

• Column grid and structural bays
• Floor-to-ceiling heights
• Floor loading, lifts and corridor widths
• Potential for mezzanine levels
• Loading access and vehicle access

Units that work with the structure are more efficient, but don’t let the structure dictate the whole mix. Ground-floor and drive-up units often carry a convenience premium, while upper floors suit smaller units that can be carried. If you’re deciding between a new build and a conversion, this step will differ significantly between the two.

A guide to common unit sizes

Size band	Typical use
Around 10–25 sq ft	Boxes, seasonal items, student belongings, archives
Around 35–50 sq ft	Contents of a studio or small room, small business stock
Around 75–100 sq ft	Contents of a one- to two-bedroom home, trade equipment
150 sq ft and above	Larger household moves, bulk business stock, larger equipment

These are rough guides. Many operators find demand is concentrated in the small-to-medium range, but that varies by area, so treat any rule of thumb as a hypothesis to test rather than a target to hit.

Unit size ranges in recent Kuboid projects

Facility	Location	Unit size range
Vault Storage	Blackpool	10–75 sq ft
Arden Self Storage	Solihull	25–100 sq ft
My Own Space	Northampton	10–150 sq ft
MoorSpace Storage Company	Huddersfield	16–175 sq ft
Astwood Storage	Redditch	25–200 sq ft

These ranges show the smallest and largest unit, not the split between them. The spread differs from site to site depending on the building and the customers it serves.

Step 4: Model scenarios

Build two or three mix scenarios and compare them. For each, estimate net lettable area against gross area, then model revenue using realistic rates and occupancy for each size. Stress-test the assumptions. What happens if larger units take twice as long to let? What if small units fill faster than expected?

Then mark it out at full scale. For our client My Own Space, the operator and Kuboid’s lead designer spent a half-day mapping the layout, then physically marked out the unit positions inside the warehouse. Seeing corridor widths and unit sizes at real scale helps you catch problems before anything is built.

Step 5: Design for flexibility

Even a well-researched mix is still a forecast. To make it easier to adjust:

• Use a consistent grid or module so units can be combined or split
• Choose partition systems designed to be reconfigured
• Position doors so that changing unit sizes doesn’t mean starting again
• Plan lighting, fire protection and access control so they don’t lock in the layout

Common mistakes

• Copying a competitor instead of studying your own space
• Overbuilding large units because they’re simpler to design
• Underestimating circulation space and the impact it has on lettable area
• Optimising only for day-one demand without room to adapt
• Having no review plan once the facility opens
• Marketing being an after thought instead of a core part of the strategy for newcomers as the market has grown in terms of competition

Review once you’re open

Track enquiries against availability, occupancy by size, time to let and rate movement. This is the real data that tells you whether the mix is working, and flexible design means you can act on it.

Real operating experience shapes the next phase, too. Arden Self Storage extended its facility as customer demand grew, and Astwood Storage designed its second, purpose-built facility to reflect the original site’s layout while introducing key improvements.

Get the mix right before you build

Unit mix touches almost every design and construction decision that follows. Kuboid has delivered over 100 self storage projects across the UK and Europe. Our consultancy, planning and design, manufacture and build and aftercare services can help you test a layout before it’s built. Talk to the Kuboid team about your project.