Rentable vs Usable Square Feet (RSF vs USF)

Usable square feet: the space you can actually use

USF is measured within the tenant's demised premises — the interior of the suite. Under the dominant BOMA methods it is measured from the inside face of the perimeter wall and from the centerline of shared corridors, excluding the thickness of the exterior wall and the common-area structure. It counts the space where desks, inventory, exam tables, or shelving actually go: offices, open floor, conference rooms, private restrooms dedicated to the suite, and storage inside the suite lines.

What gets excluded depends on the BOMA edition and the method chosen for the building. Columns, wall thickness inside the suite, floor risers, and areas with very low clear heights are subtracted or prorated under some methods and ignored under others. The same suite can measure a few percent differently under BOMA 1996 versus BOMA 2010/2017, which is why leases that matter state the standard by name rather than assuming one.

In a single-tenant building the distinction nearly disappears: when one occupant holds the whole structure, rentable and usable often converge, or the building is simply let on its gross footprint. The RSF/USF split is fundamentally a multi-tenant concept, and it is where the landlord recovers the cost of the space everyone shares but no one occupies alone.

Rentable square feet: usable plus a share of the load

RSF adds the tenant's allocated portion of the building common areas — the "load" — on top of USF. Lobby, elevator lobbies, corridors, restroom banks, janitorial and mechanical rooms, and stairwells are measured for the building as a whole and distributed across tenants, normally in proportion to their usable area. A tenant's rentable area is therefore always equal to or larger than its usable area, and it is the number that appears on the rent statement, the CAM bill, and the lease's expense-stop and pro rata share math.

The two are related by a simple formula: RSF = USF × (1 + load factor), where the load factor is the common-area share expressed as a percentage. At a 15% load, a 9,000-USF suite rents as 10,350 RSF. Worked through at dollars: a rate of $40.00 per RSF on 10,350 rentable feet is $414,000 a year — an effective $46.00 per usable square foot. Tenants comparing a "cheap" $40 on a building with a heavy load against a "pricey" $44 on a lean one need this conversion before the headline rate means anything.

The same conversion works in reverse when a deal is quoted on a usable basis, which retail and some flex buildings do more often than office. Rent per usable foot is always higher than rent per rentable foot for the same total dollars, because the smaller denominator is doing the same work. A rate is only comparable to another rate when both sit on the same measurement base.

The load factor: how it is set and where it bites

The building's load is arithmetic at the property level: total rentable area divided by total usable area. A 300,000-RSF tower enclosing 260,000 USF carries roughly a 15.4% load, and each floor's share is assigned in proportion. Newer Class A towers with grand lobbies, expansive elevator banks, and generous corridor widths run heavier loads; spartan buildings and older layouts run lighter. Because the landlord controls the common areas, the load is a structural feature of the building, not a negotiated term — but its effect on the tenant's effective rate is exactly the kind of thing tenants under-price in lease comparisons.

Two traps recur at renewal and audit time. First, a reconfiguration that adds or shrinks common area — a new fitness center, a re-clad lobby, converted mechanical space — silently moves every tenant's rentable area and every bill computed on it, even when no wall of the suite changes; leases that give the landlord re-measurement rights should be read before assuming the stated RSF is permanent. Second, expansions and contractions change a tenant's share of the load: adding a floor changes the numerator, but if the stated percentages are not restated by amendment, invoices keep billing the old rentable figure and the error compounds.

Expense allocation follows the rentable figure the same way rent does: the pro rata share that multiplies CAM, tax, and insurance pools is normally premises RSF over the building's Defined Area. A tenant negotiating the denominator is negotiating the same load question from the other side.

What to capture when abstracting or auditing RSF/USF

The measurement basis is a first-class data point of the lease, not a footnote. An abstract should record rentable area, usable area, the load factor stated or implied, the measurement standard the lease invokes (which BOMA edition and method), and which basis each obligation keys off — rent, additional-rent shares, TI allowances, and renewal rates are sometimes split across bases within one document, e.g. a TI allowance of $50 per usable foot billed against a rent stated per rentable foot.

Verification is straightforward when the numbers are captured: recompute RSF from USF and the stated load, confirm the rent roll in Yardi or MRI carries the rentable figure the lease defines, and test any re-measurement or amendment restatement against the lease's own re-measurement clause. A rent roll configured on the wrong basis — usable area into a rentable-rate field — over- or under-collects every month of the term without anyone touching a rate.