BOMA measurement standards are the ANSI-accredited rules, published by the Building Owners and Managers Association International, that define how square footage is calculated in commercial buildings. They matter because the rentable area figure they produce is what tenants actually pay rent on. The development process is accredited by the American National Standards Institute, so each standard goes through a formal consensus process before adoption.1BOMA International. BOMA Floor Standards Development Program BOMA has published measurement standards since 1915, and the current office standard was released in 2024.2BOMA International. BOMA Standards
The Six Standards and Which One Applies
BOMA maintains a separate standard for each major property type. Each carries an ANSI designation and addresses the measurement issues unique to that category.
- Office Buildings (ANSI/BOMA Z65.1). The most widely used standard. The 2024 version provides two methods for calculating rentable area and is the benchmark for nearly every office lease in the country.
- Industrial Buildings (ANSI/BOMA Z65.2). Warehouses, distribution centers, and manufacturing facilities. It focuses on exterior wall measurements and accounts for loading docks and mezzanines.
- Gross Areas (ANSI/BOMA Z65.3). A consistent method for measuring the total constructed area of any building type, including the exterior face of walls.
- Multi-Unit Residential Buildings (ANSI/BOMA Z65.4). Apartments and condominiums, separating private living quarters from shared amenities.
- Retail Buildings (ANSI/BOMA Z65.5). Shopping centers and street-front retail, with particular attention to how the storefront line is drawn and how shared pedestrian areas affect tenant charges.
- Mixed-Use Properties (ANSI/BOMA Z65.6). Integrates different occupancy types into a single report so shared infrastructure costs are distributed across office, retail, and residential tenants in the same building.
These six cover the vast majority of commercial real estate. There is no separate BOMA standard for specialty spaces like laboratories or life science facilities; those properties are measured under whichever standard best matches their primary use.3BOMA International. BOMA Floor Standards Interpretations Documents – Best Practice Guidance
Gross, Usable, and Rentable Area
Three area terms interact in sequence, and the last one is what you pay on.
Gross Building Area is the total constructed footprint, measured to the outside face of the exterior walls. It includes everything inside the building envelope. This figure matters for valuation and construction but is not the rent basis.
Usable Area is the private space a tenant occupies. It’s the carpeted area behind your suite door where furniture and equipment go. It excludes building-wide common areas like elevator lobbies, stairwells, and shared restrooms.
Rentable Area is Usable Area plus a proportional share of the building’s common spaces. Every tenant pays for a slice of the lobbies, hallways, and shared restrooms, even though no one’s desk sits there. The gap between usable and rentable square footage is where most lease disputes originate.
The Load Factor
The load factor, sometimes called the R/U ratio, is the multiplier that converts Usable Area into Rentable Area. If your usable space is 5,000 square feet and the building’s load factor is 1.12, your rentable area is 5,600 square feet, and you pay rent on all 5,600. Office load factors commonly fall between 1.10 and 1.15, though buildings with generous lobbies, conference centers, or other amenities can push higher. A load factor of 1.15 means 15 percent of your rent covers shared space you don’t exclusively control.
Major Vertical Penetrations
Major vertical penetrations are floor openings larger than one square foot that serve building systems or occupant functions, such as elevator shafts, stairwells, and large mechanical chases. They are excluded from rentable area because no tenant can use them. Small penetrations of one square foot or less, like individual pipe runs or conduit sleeves, are not classified as major vertical penetrations, even when several are grouped together in the same enclosure.3BOMA International. BOMA Floor Standards Interpretations Documents – Best Practice Guidance
Method A vs. Method B Under the Office Standard
The Office Standard offers two ways to calculate rentable area. Both must be disclosed, and the choice has to be made before measurements begin.2BOMA International. BOMA Standards
Method A uses multiple load factors: one for each floor and one for building-wide common areas. Shared spaces on a given floor are allocated only to tenants on that floor, and building-level common areas like the main lobby are allocated across all tenants. This produces lower load factors on efficient single-tenant floors, but those factors shift whenever a floor is reconfigured or a tenant moves in or out.
Method B applies a single load factor across the entire building. All shared space, floor-level and building-level, is rolled into one number. The result is a higher load factor on single-tenant floors than under Method A, but it’s more stable because floor reconfigurations don’t change the building-wide ratio.
For tenants, the trade-off is predictability versus precision. Method B is simpler and more predictable, which is why many institutional landlords prefer it. Method A can favor tenants on efficiently laid-out floors, though that advantage can disappear when suites on their floor are reconfigured.
How the Measurement Is Done
Accurate measurements start with the most recent architectural blueprints or CAD files. If the drawings are outdated or unavailable, a field survey from scratch adds considerable time and cost.
The boundary of each floor is set at the dominant portion of the inside finished surface of the exterior wall. In practice, that means measuring to the interior face of the wall or to the glass line of the windows, whichever occupies more than 50 percent of the floor-to-ceiling height. In a modern curtain-wall building where floor-to-ceiling glass dominates, the measurement goes to the glass. In an older masonry building, it goes to the interior wall surface. Where two tenants share a wall, the boundary falls at the centerline of that wall.
Technicians verify the drawings on-site, walk each floor to confirm renovations and new buildouts are captured, and then apply the standard’s formulas to generate the load factor and final rentable area for each suite. The output is a certified BOMA floor plan report with color-coded diagrams and a summary of calculated areas, which can be attached to leases, appraisals, or loan packages. Licensed architects, surveyors, or specialized measurement firms typically perform and sign these reports. BOMA International does not certify specific software or individual practitioners, so the credibility of the report depends on the qualifications of the professional who produces it.
When to Remeasure
A BOMA measurement is not a one-time event. The clearest trigger is a significant renovation: adding or removing walls, expanding into adjacent space, or converting a floor’s use. Lease renewals and property sales are equally important. When a building changes hands, the new owner often remeasures to reset the rent roll, and tenants without negotiated protections may see their rentable area change. A new edition of the standard itself can also shift numbers, though whether a standards update triggers recalculation depends on the lease.
Lease provisions vary widely. Some landlord-drafted leases grant the landlord unilateral authority to remeasure at any time. Tenants with leverage can secure a mutual right to remeasure or lock in a fixed rentable area that isn’t subject to change. A well-drafted clause typically sets a threshold percentage that must be exceeded before rent adjusts and specifies who pays for the survey.
What Measurement Errors Cost
Discrepancies are more common than tenants realize, and small errors compound over a long lease. In one documented case, an office tenant discovered their 4,400-square-foot suite was actually 800 square feet smaller than the lease stated, translating to roughly $50,000 in overpaid rent over a five-year term. In another, a 27-square-foot discrepancy in a high-rent downtown shopping mall cost a tenant $20,000 over seven years. The industry calls this phantom space, and it inflates both base rent and common area maintenance charges.
When a discrepancy is identified, the landlord may be required to reimburse past overpayments and adjust future rent. These errors are more often the result of outdated floor plans or sloppy initial measurements than deliberate fraud, but the financial impact is the same. Measurement accuracy also affects property valuation, because investors and lenders rely on verified square footage to calculate revenue potential, set loan-to-value ratios, and appraise assets.
Protecting Yourself as a Tenant
A few steps prevent measurement-related overpayment. Request the building’s current BOMA measurement report and confirm which standard and method were used. If the report is more than a few years old or predates recent renovations, treat that as a warning sign. Negotiate a remeasurement clause that lets you hire your own architect or surveyor to verify the landlord’s numbers within a specified window after the lease starts; typical provisions allow 60 days to initiate a remeasurement. Insist on a threshold percentage in the clause, so minor differences don’t trigger costly disputes but meaningful errors do get corrected.
If a dispute arises, many remeasurement provisions call for both parties’ architects to negotiate, and if they can’t agree, a neutral third architect makes the final determination. Knowing that process exists before you sign is far better than discovering it after you suspect you’ve been overpaying for years.