Loss factor is the percentage of a tenant's rentable square feet that is not usable, representing the share of common areas built into the rent. It is calculated as rentable square feet minus usable square feet, divided by rentable square feet. A higher loss factor means a tenant pays for more space it cannot occupy.
How Is Loss Factor Calculated?
Loss factor is calculated by subtracting usable square feet from rentable square feet, then dividing that difference by rentable square feet. The formula is Loss Factor = (Rentable SF minus Usable SF) divided by Rentable SF. Per PropertyMetrics, a suite with 10,000 rentable and 8,000 usable square feet has a loss factor of 20%.
Loss factor expresses the same relationship as load factor but from the rentable base rather than the usable base, so the two percentages are not equal for the same space. Loss factor divides the common area by rentable square feet; load factor divides rentable by usable. This distinction is the single most common source of confusion in office measurement.
Input | Definition |
Rentable square feet (RSF) | Total area rent is charged on, usable plus common area share |
Usable square feet (USF) | Area the tenant occupies exclusively |
Common area (RSF minus USF) | The unusable portion of rentable space |
Loss factor | Common area divided by rentable square feet, as a percentage |
Loss factor is standard-dependent. Per CommercialCafe, most of the U.S. follows BOMA, while New York City follows REBNY, which measures to the exterior face of the window and produces higher loss factors. That is one reason Manhattan figures run above the national average.
Why Loss Factor Matters
Loss factor matters because it directly measures how much of a rent bill buys space the tenant cannot use, and it varies enough between buildings to change which deal is cheaper. A 5-point swing in loss factor on a 10,000 rentable-foot suite is 500 square feet of paid-for area that never appears in the tenant's usable footprint.
Per CommercialCafe, Manhattan loss factors average 20% to 35%, with full-floor space commonly around 27% and multi-tenant floors reaching 38% to 39%. A Class A Midtown building might carry a loss factor above 30% while a comparable Dallas or Denver building sits closer to 22%. For an operator, normalizing competing offers to usable square feet strips out the loss factor and reveals the true cost of occupancy.
The quotable point for a tenant rep: loss factor is the tax you pay on space you will never occupy, and it is negotiable only to the extent the building's measurement lets it be.
Example
A tenant leases a suite quoted at 12,000 rentable square feet. A test fit shows 9,000 usable square feet. The loss factor is 12,000 minus 9,000, divided by 12,000, which equals 25%. At $50.00 per rentable square foot, annual rent is $600,000, and the effective cost per usable foot is $600,000 divided by 9,000, which equals $66.67.
Step | Calculation | Result |
Common area | 12,000 - 9,000 | 3,000 |
Loss factor | 3,000 / 12,000 | 25% |
Annual rent | 12,000 x $50.00 | $600,000 |
Effective rent per usable foot | $600,000 / 9,000 | $66.67 |
The tenant pays on 12,000 square feet but occupies 9,000. The 25% loss factor turns a $50.00 rentable rate into $66.67 per usable foot, the number that reflects true occupancy cost.
Variations and Edge Cases
Loss factor is not one number: it depends on floor type, measurement standard, and how the building allocates common area. Full-floor tenants absorb less shared corridor, while multi-tenant floors carry the highest loss factors. The table below separates the variants an operator should confirm.
Variant | Treatment |
Full-floor tenant | Lower loss factor; Manhattan full floors commonly around 27% |
Multi-tenant floor | Higher loss factor, reaching 38% to 39% in dense markets |
BOMA standard | Governs most U.S. markets; loss factors tend to run lower |
REBNY standard | Measures to exterior face; produces higher loss factors, common in NYC |
Building re-measurement | A re-measured building can raise loss factor and rent at renewal |
The common mistake is confusing loss factor with load factor. They describe the same common area from different denominators, so a 20% loss factor and a 20% load factor are not the same suite.
Loss Factor vs Load Factor
Loss factor is often confused with load factor, and the two use the same inputs but different denominators. Loss factor is common area divided by rentable square feet. Load factor is rentable square feet divided by usable square feet, expressed as the percentage above 1.0. For the same suite, the loss factor is always lower than the load factor percentage.
Per Building Engines, a suite with 10,000 rentable and 8,000 usable square feet has a loss factor of 20%, computed as 2,000 divided by 10,000. Its load factor is 10,000 divided by 8,000, which equals 1.25, or 25% added on. Same space, same 2,000 square feet of common area, two different percentages. Always confirm which one a quote uses.
Frequently Asked Questions
What is a loss factor in commercial real estate?Loss factor is the percentage of a tenant's rentable square feet that is not usable, representing the common area share built into rent. It equals rentable square feet minus usable square feet, divided by rentable square feet. A 25% loss factor means a quarter of the paid-for space is common area.
What is the difference between loss factor and load factor?Loss factor is common area divided by rentable square feet, while load factor is rentable square feet divided by usable square feet. For the same suite the two percentages differ: a space with 10,000 rentable and 8,000 usable square feet has a 20% loss factor but a 25% load factor.
What is a typical office loss factor?Per CommercialCafe, Manhattan loss factors average 20% to 35%, with full floors commonly around 27% and multi-tenant floors reaching 38% to 39%. Markets following the BOMA standard, such as Dallas or Denver, often sit closer to 22%.
Related Terms
Rentable Square Feet
Usable Square Feet
Price Per Square Foot
Net Effective Rent
Common Area Maintenance