What Is Loss Factor in Commercial Real Estate?

When you lease office space, the number of square feet on your lease is almost never the number of square feet you actually use. The difference between those two figures is captured by a metric called the loss factor, and understanding it is one of the most practical things you can do before signing a commercial lease.

The loss factor tells you what percentage of the space you are paying for is taken up by shared or common areas rather than your own workspace. A higher loss factor means you are paying for more space you do not exclusively occupy. It is not a hidden fee or a trick, but it is one of the most commonly misunderstood parts of commercial leasing, and failing to account for it can mean budgeting for one amount of usable space and ending up with meaningfully less.

Key Takeaways

• What Loss Factor Measures: The percentage of your leased space that goes to common areas (lobbies, hallways, elevators, restrooms) rather than your exclusive workspace.
• The Formula: Loss Factor = (Rentable Square Feet – Usable Square Feet) / Rentable Square Feet. A 10,000 RSF lease with 8,000 USF has a 20% loss factor.
• Loss Factor vs. Load Factor: These are related but different calculations. Loss factor is a percentage of the total; load factor is a ratio (RSF / USF). Both describe the same relationship from different angles.
• Typical Ranges: Loss factors generally run from 15% to 30%, depending on building class, age, and location. Class A buildings with large lobbies and extensive amenities tend to fall at the higher end.
• BOMA 2024 Changes: The updated BOMA measurement standard now includes certain outdoor amenities in rentable area and has changed how unenclosed spaces like balconies and terraces are calculated.

Rentable Square Feet vs. Usable Square Feet

Before loss factor makes sense, you need to understand the two measurements it is built from.

Rentable square feet (RSF) is the total area you pay rent on. It includes your private workspace plus a proportional share of the building’s common areas: lobbies, hallways, elevator shafts, stairwells, restrooms, mechanical rooms, and any other shared spaces. This is the number that appears on your lease and the number your rent is calculated against.

Usable square feet (USF) is the space you actually occupy and control. For a tenant leasing a full floor, USF typically includes everything on that floor, including restrooms and elevator lobbies, because no other tenant shares them. For a tenant leasing part of a floor, USF covers only the area within the walls of the leased suite.

The gap between those two numbers is what loss factor measures. If you are comparing two listings with similar rental rates per square foot, the one with the lower loss factor will give you more workspace for the same money. For a closer look at how RSF, USF, and load factors feed into what you actually pay each month, see our guide on how to calculate commercial rent.

How Loss Factor Is Calculated

The formula is straightforward:

For example, if your lease is for 10,000 rentable square feet and the usable area within your suite is 8,000 square feet:

That means 20% of the space you are paying for is allocated to common areas rather than your exclusive workspace.

The last line is the one that catches tenants off guard. Your rent is quoted on the rentable figure, but the effective cost per usable square foot is higher. In this example, you are paying $30 per rentable square foot but $37.50 for every square foot you actually use.

Loss Factor vs. Load Factor

You will often see these two terms used interchangeably, but they are calculated differently and the distinction matters when you are comparing numbers across markets or brokers.

Loss factor is expressed as a percentage: (RSF – USF) / RSF. Load factor (sometimes called the add-on factor) is expressed as a ratio: RSF / USF.

Using the same example: if RSF is 10,000 and USF is 8,000, the loss factor is 20% and the load factor is 1.25. Loss factor is more commonly used in New York City and the tristate area, while load factor is the standard in most other U.S. markets and is the basis of BOMA’s measurement methodology. When comparing spaces or speaking with brokers, confirm which metric is being used.

BOMA vs. REBNY: Two Measurement Standards

In the U.S., two organizations set the standards for how office space is measured: the Building Owners and Managers Association (BOMA) and the Real Estate Board of New York (REBNY).

Most of the country follows BOMA’s standards. New York City and the surrounding tristate area largely follow REBNY’s. The practical difference comes down to where the measurement begins: BOMA measures from the centerline of the exterior window, while REBNY measures from the exterior face of the window. That distinction adds square footage under REBNY’s method, which is one reason loss factors in New York tend to run higher than the national average.

BOMA updated its office measurement standard in 2024 (ANSI/BOMA Z65.1-2024), and the changes are worth knowing about if you are evaluating a lease in a building measured under the new rules. The key updates include:

• Ground-level outdoor amenities such as patios and terraces built for tenant use are now included in the building’s rentable area, even if they are uncovered.
• Tenant balconies and terraces no longer carry a load factor. Under the previous standard, these spaces had common area costs allocated to them the same way interior space did. Under the 2024 standard, they are calculated without a load factor, which can slightly reduce the overall loss factor for tenants with access to these spaces.
• A new category called Non-Allocated Tenant Areas now covers unenclosed tenant spaces, storage areas, and single-tenant shafts. These are included in rentable area but are not subject to load factor calculations.

These updates generally benefit landlords by increasing measurable rentable area while giving tenants clearer treatment of valuable outdoor amenities.

If you are comparing two buildings and one has been remeasured under the 2024 standard while the other uses the older 2017 or 2010 standard, the loss factors may not be directly comparable. Always ask which measurement standard applies to the building you are evaluating.

Typical Loss Factors by Building Class

Loss factors vary significantly depending on the type of building, its age, and its location. Buildings with grand lobbies, extensive amenity packages, and multiple elevator banks will naturally have higher loss factors than straightforward, no-frills properties.

In New York City, loss factors tend to run 5 to 10 percentage points higher than national averages across all building classes, driven by the combination of REBNY measurement standards and the premium common area finishes typical of the market. A Class A building in Midtown Manhattan might carry a loss factor above 30%, while a comparable building in Dallas or Denver might sit closer to 22%.

For a broader look at what distinguishes these building tiers, see our guide to understanding Class A, Class B and Class C office buildings.

What Affects Loss Factor

No two buildings produce the same loss factor, and knowing what drives the number up or down can help you make sense of what you are seeing in the market:

Building design and age. Older buildings with irregular floor plates, thick load-bearing walls, and oversized mechanical rooms tend to have higher loss factors. Newer buildings designed with efficient cores can keep loss factors lower, though this is sometimes offset by the larger lobbies and amenity spaces that modern tenants demand.

Floor size and layout. Larger floor plates generally produce lower loss factors because the common areas (elevator lobbies, restrooms, corridors) represent a smaller share of the total area. A 30,000-square-foot floor will typically have a lower loss factor than a 10,000-square-foot floor in the same building.

Full-floor vs. part-floor tenancy. If you lease an entire floor, common areas like restrooms and elevator lobbies become part of your usable space, which lowers the loss factor. Part-floor tenants share those spaces with other tenants on the same floor, raising the loss factor.

Amenity investment. The flight-to-quality trend in the office market has led many landlords to invest heavily in building amenities: fitness centers, tenant lounges, conference centers, rooftop terraces, food halls. These spaces improve the tenant experience, but they also increase the building’s common area footprint and, with it, the loss factor.

Market conditions. When demand is strong and vacancy is low, some landlords adjust their loss factors upward. This effectively increases the rentable area and the resulting rent without changing the quoted rate per square foot. When the market softens, landlords may be more willing to negotiate or hold loss factors steady.

How to Evaluate Loss Factor When Leasing

Loss factor is one piece of the puzzle when you are comparing office spaces, but it is an important one. Here is how to approach it practically:

Ask for both RSF and USF. Not all listings or proposals include usable square feet. If the number is not provided, request it. You cannot evaluate the loss factor without both figures.

Calculate your effective rent. Divide your total annual rent by the usable square feet to see what you are actually paying per square foot of workspace. This is the number that should drive your comparison across spaces, not the quoted rate per rentable square foot.

Ask which measurement standard was used. BOMA or REBNY will produce different results for the same building. If you are comparing spaces in different markets, this matters.

Request a floor plan. A floor plan lets you see exactly where the common areas are and how the usable space is configured. It can also reveal whether the layout is efficient for your needs or whether you will lose additional workspace to awkward column placements or odd-shaped corridors. If you are still getting comfortable with the terminology that appears in commercial listings, our guide to reading an office space listing breaks down the key terms.

Consider hiring a space planner. For larger leases, an independent space planner can verify the landlord’s measurements, identify inefficiencies, and confirm that the loss factor is consistent with market norms for the building class.

Negotiate. Loss factor is not always fixed. In softer markets or for larger tenants, landlords may be willing to cap the loss factor in the lease, agree to remeasurement, or offer concessions that offset a high loss factor.

For more on evaluating office space before you commit, see our guide to finding office space for your small business and our list of questions to ask before leasing office space.

Find Office Space

Understanding loss factor is an important step in making sure you are comparing office spaces on equal terms. CommercialCafe provides comprehensive commercial real estate listings that allow you to compare office spaces, coworking options, and industrial properties across the U.S. Start your search by filtering for your target city and the features that matter most to your business.

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Frequently Asked Questions (FAQ)

Q: What is a “good” loss factor?
A: There is no universal answer because it depends on the building class and market. As a general benchmark, anything below 20% is considered efficient for a Class B or C building. For Class A buildings with significant amenities, 20% to 25% is typical. In New York City, loss factors above 25% are common and not unusual for premium space.

Q: Can the loss factor change during my lease?
A: It can if the building is remeasured, renovated, or if common areas are reconfigured. Some leases lock in the loss factor for the term; others allow the landlord to adjust it. Check your lease language carefully, particularly any clauses related to remeasurement or changes to the building’s common areas.

Q: Is loss factor the same as load factor?
A: They describe the same relationship but are calculated differently. Loss factor is a percentage: (RSF – USF) / RSF. Load factor is a ratio: RSF / USF. A 20% loss factor is equivalent to a 1.25 load factor. Loss factor is more common in the New York market; load factor is standard in most other U.S. markets.

Q: Does loss factor apply to industrial or retail space?
A: The concept is most relevant to office leasing, where common areas like lobbies, elevator banks, and shared conference facilities represent a significant share of the building’s total area. Industrial and retail spaces are typically leased on a more straightforward square footage basis, though BOMA publishes separate measurement standards for those property types as well.

Q: How did the BOMA 2024 standard change loss factor calculations?
A: The most notable changes are that certain outdoor amenities (patios, terraces) now count toward rentable area, tenant balconies no longer carry a load factor, and a new category of Non-Allocated Tenant Areas (storage, single-tenant shafts) is included in rentable area but not subject to load factor calculations. These changes can affect the loss factor for buildings remeasured under the new standard.

Q: Should I avoid buildings with high loss factors?
A: Not necessarily. A high loss factor often reflects extensive amenities that benefit your employees and clients. A building with a 28% loss factor but a full fitness center, conference facilities, and a premium lobby may be a better value than a building with a 17% loss factor and no amenities. Evaluate loss factor alongside what the common areas actually provide.

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