Office Space Terms: Usable vs. Rentable Square Footage
Commercial square footage isn't measured the way you'd think. The real difference between usable and rentable square footage, and why it matters for your rental budget.
A common misconception is that commercial real estate works the same way as leasing an apartment. Some basic terms apply to both, but there are real differences worth understanding — starting with how square footage is measured, and what you're actually paying for.
Usable square footage (USF) is the space exclusively occupied by your team. Rentable square footage (RSF) adds a proportional share of the building's common areas, like hallways and lobbies, and is what your rent is actually calculated on. RSF is always larger than USF, so simply measuring your own suite and multiplying by the quoted rate will understate your true cost.
Why It's Not as Simple as Measuring Your Suite
Commercial space is measured very differently than residential space, and it directly affects what you actually pay. To make commercial space easier to compare, buildings advertise a dollar amount per square foot, then charge each tenant based on how much of the building they occupy relative to the whole.
A common misconception: that you can measure your own suite and calculate your monthly rent directly from it — Cost = Rate/SF × Measured SF. It's a reasonable assumption, but it's not how commercial rent actually works.
The answer lies in two distinct terms: Usable Square Footage and Rentable Square Footage. When you measure your own suite, you're getting a rough estimate of usable square footage — but rental rates are actually determined by rentable square footage, a different, larger number.
Usable Square Footage
In its simplest sense, usable square footage is the amount of space in a tenant's private suite — in theory, exactly what you'd measure yourself. The difference comes from how landlords are required to measure it.
Landlords measure USF under standards set by the Building Owners and Managers Association (BOMA), which allow measurement halfway into common walls, up to the dominant portion of exterior walls, without deducting for columns. A number of other technical factors can shift the actual figure too — measuring USF is trickier, and more easily misleading, than it first appears.
Rentable Square Footage
Even once USF is determined, it's not what your rent is actually based on. Rentable Square Footage (RSF) is what landlords advertise, and it's what the quoted rate per square foot actually applies to.
Not every part of a building is divided into individual suites. Common areas — hallways, stairs, conference rooms, elevator lobbies — indirectly benefit every tenant in the building. These get factored in by multiplying your USF by a proportional share of the total building square footage, a percentage commonly called the "load factor."
RSF includes your pro-rata share of common areas, and it's always larger than USF. When comparing options in the market, the gap between usable and rentable square footage can have a real, meaningful impact on your rental budget — it's worth confirming both figures, not just the headline rate, for any space you're seriously considering.
For more commercial lease vocabulary, see Key Terms in a Commercial Lease Agreement.
Know Exactly What You're Paying For
A local tenant rep can calculate the real USF, RSF, and load factor on any space you're considering — before you sign anything.
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