Supply per head means nothing on its own. Divided into demand, it gives the occupancy a catchment can hold.
Self-storage square feet per capita is the net rentable area of every store in the catchment divided by the people who live in it. In an illustrative catchment of 145,000 people with 220,000 sq ft of storage it is 1.52 sq ft per capita. On its own that number says nothing; set beside demand of 1.30 sq ft a head it says the market is 86.0 per cent occupied today and, once 65,000 sq ft of new stores open, 68.4 per cent.
Worked in full in Self-Storage Real Estate by Julian R. Sterling, with every figure reproduced in a free workbook.See the book on Amazon →
Supply per capita is the first figure in almost every self-storage feasibility study, usually set against a national average to show that the area is "under-stored". The comparison is weak, because national figures differ by several times between countries and by a wide margin between towns in the same country, for reasons of housing size, renting and business mix that have nothing to do with the site. What turns the ratio into a decision is the second number: the square feet the catchment's households and businesses actually rent. Divide one by the other and you have the occupancy the market can hold, which is the number a lease-up plan depends on.
| Store or input | Value |
|---|---|
| Store A | 62,000 sq ft |
| Store B | 55,000 sq ft |
| Store C | 46,000 sq ft |
| Store D | 35,000 sq ft |
| Container yard E | 22,000 sq ft |
| Existing supply, net rentable | 220,000 sq ft |
| Under construction | 20,000 sq ft |
| Proposed store (the site) | 45,000 sq ft |
| Population; persons per household | 145,000; 2.3 |
| Households renting a unit | 4.0% |
| Average area rented per household | 60 sq ft |
| Share of occupied area rented by businesses | 20% |
| Population growth, a year | 1.0% |
Step 1. Supply per capita
Net rentable area, not gross building area: 220,000 / 145,000 = 1.52 sq ft per person.
Step 2. Demand in square feet
Households: 145,000 / 2.3 = 63,043. Renting: 63,043 × 4.0% = 2,522. Domestic area: 2,522 × 60 = 151,304 sq ft. Grossed up for business customers: 151,304 / (1 − 20%) = 189,130 sq ft, 1.30 sq ft per person.
Step 3. The occupancy the market holds
189,130 / 220,000 = 86.0 per cent. In Excel, with named cells: =Population/HH_size*Penetration*Area/(1-Business_share)/Supply.
Step 4. Roll forward with the pipeline
In three years the population is 149,394 and demand 194,861 sq ft. Supply with the scheme under construction is 240,000 sq ft, 1.61 per capita, and occupancy 81.2 per cent. Add the proposed store and supply is 285,000 sq ft, 1.91 per capita, and occupancy 68.4 per cent.
Step 3 is also the calibration test. Walk the competitors, count their vacant units and estimate their occupancy. If the stores are in fact around 86 per cent let, the penetration and unit size are plausible. If they are 95 per cent let, demand is understated; if 70 per cent, overstated. Adjust the inputs until the model reproduces the market you can see before you ask it about the one you cannot.
The catchment is not under-stored today. At an 88 per cent target occupancy it can support 214,921 sq ft and has 220,000, so it is 5,079 sq ft over before anything new opens. The pipeline adds 65,000 sq ft while population growth adds 5,731 sq ft of demand: more than eleven square feet of new supply for every new square foot of demand. If the five existing stores and the two new ones end at the same occupancy, the proposed 45,000 sq ft store fills 30,768 sq ft. Its lease-up has to be won from competitors on price, and the pace at which that happens is the subject of how long a self-storage lease-up takes.
| Households renting | 50 sq ft | 60 sq ft | 75 sq ft |
|---|---|---|---|
| 3.0% | 42.7% | 51.3% | 64.1% |
| 4.0% | 57.0% | 68.4% | 85.5% |
| 5.0% | 71.2% | 85.5% | 106.8% |
| 6.0% | 85.5% | 102.6% | 128.2% |
Cells above 100 per cent mean the inputs describe a market that would be full with waiting lists, which the competitor walk would have shown. The table is steep: one point of penetration moves occupancy by about 17 points. To hold 88 per cent with the full pipeline, penetration would have to rise from 4.0 to 5.1 per cent. New, visible, modern stores do raise usage in a catchment, so that rise is possible, but it is a forecast about behaviour and should be underwritten as one, not hidden inside a per-capita benchmark.
Comparing supply per capita with a national average and concluding that a low figure means unmet demand. A catchment can sit well below the national number and still be full, because its households are fewer, older or more often owners with garages; it can sit above it and still have waiting lists, because it has more renters, more small flats and more small businesses. The ratio only becomes evidence when it is divided into an estimate of demand that has been calibrated to the occupancy the existing stores actually achieve.
Count net rentable area, not gross building area, and include container yards and the storage floors of removals firms if they compete for the same customers. Excluding them flatters the ratio and the occupancy forecast at the same time.
The free workbook for this case takes the catchment from the planning register and the competitor walk into the store's own lease-up, and the self-storage financial model template carries the occupancy that results into income and value.
There is no portable benchmark, because usage varies widely between countries and towns. The useful test is supply against local demand. In an illustrative catchment, 1.52 sq ft per capita of supply against 1.30 of demand means 86.0 per cent occupancy today; with the pipeline, 1.91 sq ft per capita gives 68.4 per cent, which a new store would struggle to lease into.
Multiply households by the share renting a unit and the average area each rents, then gross up for business customers. Here 63,043 households at 4.0 per cent renting 60 sq ft give 151,304 sq ft, and a 20 per cent business share takes demand to 189,130 sq ft. Calibrate the inputs until they reproduce the occupancy the competitors actually show.
Divide demand by a target occupancy and subtract existing supply. With 189,130 sq ft of demand and an 88 per cent target, the illustrative catchment supports 214,921 sq ft against 220,000 already built, so it has no headroom. Absorbing the full pipeline at 88 per cent would need household penetration to rise from 4.0 to 5.1 per cent.
This article is one calculation from Self-Storage Real Estate. The book takes the same case from first principles to the decision, chapter by chapter, and every figure it prints is a live formula in the free companion workbooks.
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