The number on the lease and the number you can stand in

When a broker tells you a suite is "5,000 square feet," you picture 5,000 square feet of floor — walls you can paint, desks you can arrange, a window line you can pace off. So it comes as a quiet shock the first time you actually tape-measure the space and find something closer to 4,300. Nobody lied to you. You were simply quoted the rentable area, and you were imagining the usable one. The gap between those two numbers has a name, it has a formula, and over a ten-year term it can quietly add up to a year or more of rent you never connected to anything you could walk on.

This is one of the most consequential ideas in a commercial lease, and it almost never gets explained plainly. So let's do that.

Two measurements, two very different jobs

Usable square footage is the space inside your suite — the area your team occupies. Roughly, it's what you'd measure if you walked the demising walls of your own four corners. It's the honest answer to "how much room do we actually have?"

Rentable square footage is usable square footage plus your proportional share of the building's common areas: the lobby, the elevator banks, the shared corridors, the public restrooms, the mechanical and electrical rooms, sometimes the loading dock. The logic is that a tenant doesn't just consume their own suite; they consume the building that makes the suite reachable, lit, and code-compliant. So the landlord spreads the square footage of those shared spaces across every tenant and bills accordingly.

Your rent is calculated on the rentable number. Always. The usable number is the one that determines whether your people fit.

The load factor is the multiplier between them

The ratio that converts usable into rentable goes by several names — load factor, common area factor, add-on factor, or the R/U ratio (rentable-to-usable). They all describe the same thing: the percentage of common area layered on top of your usable space.

The math is simple once you see it:

Rentable SF = Usable SF × (1 + Load Factor)

So if your usable area is 4,300 square feet and the building carries a 16% load factor, your rentable area is 4,300 × 1.16 ≈ 4,988 — call it the 5,000 you were quoted. You pay rent on roughly 700 square feet you can never put a desk in.

Load factors commonly land somewhere in the low double digits for efficient buildings and climb higher in buildings with grand lobbies, lots of elevators, or unusual floor shapes. A trophy tower with a soaring atrium is expensive to share, and that expense arrives as a higher load factor. There is no universal "right" number — but there is a knowable number for your specific building, and the difference between a 12% factor and a 20% factor on the same usable space is enormous.

Where the standard comes from

These measurements aren't folklore. Most institutional landlords measure to a published standard from BOMA (the Building Owners and Managers Association), which defines precisely how to count usable area, how to allocate floor common areas versus building common areas, and how to compute the resulting ratios. The standard exists exactly because, left unregulated, "square footage" is an opinion. BOMA turns it into a method.

Knowing a standard exists is your leverage. The right question to a landlord or broker is not "is this 5,000 feet?" but "what measurement standard was used, what's the usable area, and what's the load factor that gets us to the rentable number?" A building measured to a current BOMA standard can produce those three figures on request. Vagueness in response to that question is itself information.

The trap: full-floor vs. multi-tenant floors

Here's a subtlety that catches even experienced tenants. The load factor isn't fixed per building — it can differ floor by floor, and it interacts with how a floor is divided.

When you lease an entire floor, the corridors and restrooms on that floor are yours in the sense that no neighbor shares them, so the way common area gets allocated changes. When you take a partial floor, you share that floor's corridors and core with other tenants, and you pick up an allocation of building-wide common areas on top. Two suites with identical usable footage — one a full small floor, one a slice of a large floor — can carry meaningfully different load factors and therefore different rent for the same desks.

This is why comparing two spaces on rentable square footage alone is misleading. A suite quoted at a lower rent per rentable foot can cost you more per usable foot if its load factor is heavier. The only apples-to-apples comparison is rent per usable square foot: take the annual rent, divide by the usable area, and compare those numbers across options. That single calculation reorders most shortlists.

How to actually check it

You don't need to be a surveyor. You need three things in writing and a calculator.

First, get the usable square footage stated explicitly, not just the rentable figure. If only the rentable number is offered, ask for the load factor and back into usable: Usable = Rentable ÷ (1 + Load Factor).

Second, get the load factor named as a percentage and ask which standard produced it. Then sanity-check it against the building type. An unremarkable mid-rise carrying a load factor far above its peers deserves a question.

Third, re-run the comparison on usable terms. Build a tiny table: each option's rentable rent, its usable area, and the resulting rent per usable foot. The space that looked cheapest by the headline number frequently isn't.

And remember that the load factor compounds with everything else. Your share of operating expenses, your CAM allocation, your proportionate share of taxes — many of these are also computed on rentable square footage. A load factor that's a few points high doesn't just inflate base rent; it inflates your slice of every pass-through expense for the life of the lease.

Why this is worth an afternoon

The load factor is invisible precisely because it's baked into the one number everyone quotes. It never appears as a line item you can dispute. It's not a charge — it's a definition, agreed to the day you sign, and it silently scales every dollar that flows through the lease afterward. An afternoon spent confirming usable area, naming the load factor, and recomputing rent per usable foot is one of the highest-leverage things a tenant can do before signing, and one of the easiest to skip.

That's the whole discipline behind Closeout: turning the parts of a commercial lease that hide inside definitions and reconciliations into numbers you can actually see and check. Closeout helps you capture the usable and rentable figures, surface the implied load factor, and carry those same square-footage assumptions through to your operating-expense and CAM allocations — so the number you signed and the numbers you're billed stay connected. If you'd rather walk into the lease knowing exactly what you're paying for the floor you can stand on, take a look at closeout.lumenlabs.works.