Rentable vs Usable Square Feet: What Is a Load Factor?

When a landlord quotes the size of an office suite, the figure is almost always rentable square feet. It is the number that rent, operating expenses and often the construction allowance are multiplied by. It is not the amount of floor you can furnish.

• Usable square feet (USF): broadly, the floor area within the walls of your suite, the space your team occupies exclusively.
• Rentable square feet (RSF): your usable area plus an allocated share of the parts of the building that all tenants use or benefit from.
• Load factor: the relationship between the two. It may be expressed as a percentage added to the usable area or as a ratio of rentable to usable. You may also hear it called the add-on factor, common area factor or loss factor, and the terms are not used identically in every market.

The basic arithmetic is that rentable area equals usable area increased by the load factor. If you know any two of the three figures, you can work out the third.

A multi-tenant office building cannot function without shared space. Tenants need a lobby to enter through, corridors to reach their suites, restrooms, elevator lobbies, and rooms for the building's mechanical, electrical and telecommunications equipment. Many buildings also have shared amenities such as a conference center, fitness room or tenant lounge.

The owner has to recover the cost of building and running those areas. Instead of charging a separate fee, the industry convention is to allocate them among tenants in proportion to the space each occupies and include the allocation in the area on which rent is charged.

Common areas are often described in two layers. Floor common areas serve the tenants on one floor, such as that floor's corridor and restrooms. Building common areas serve everyone, such as the main lobby and amenity spaces. A tenant that leases an entire floor usually occupies what would otherwise be corridor, so its load can differ from that of a tenant sharing a floor with others.

A load factor is not a fee you can negotiate away. It is a property of the building's design and how the owner measures it. What you can do is account for it when comparing options.

Measurement follows a method, and the method matters. The most widely referenced standards for office buildings in the United States are published by BOMA International, the Building Owners and Managers Association. Its current office standard, BOMA 2024 for Office Buildings, carries the designation ANSI/BOMA Z65.1-2024 and sets out methods of measurement with a focus on rentable area calculations.

Three practical points follow from this.

• Not every building uses the same standard or the same edition. Older leases and older buildings may be measured under earlier versions, and some owners use their own method.
• Some markets have local conventions that differ from the published standards.
• The standards have changed over time in what counts as rentable, so two buildings measured under different editions are not directly comparable on rentable area alone.

A lease should state the rentable area of the premises, and ideally how it was measured. If the figure matters to your economics, which it does whenever rent is charged per square foot, ask which standard was used and whether you have a right to verify the measurement. Have your attorney review how the lease treats remeasurement, since some leases allow the landlord to remeasure and adjust the area during the term.

Two suites quoted at the same rentable size can hold different numbers of people. The building with the higher load factor gives you less usable floor for the same rent. Put the other way, to seat the same team you would need to lease more rentable area there, and pay for it.

This is why the quoted rent per rentable square foot is a poor basis for comparing buildings. A lower rate in a building with a high load can cost more per usable square foot, and more per person, than a higher rate in an efficient building.

A higher load is not automatically bad. It often reflects a generous lobby, wide corridors or shared amenities that your team may value and that may spare you from building a large conference room or a kitchen of your own. The point is to know what you are paying for and decide whether it is worth it.

Even usable area overstates what you can furnish. The shape of the floor and the features inside your suite determine how much of it works.

• Columns: closely spaced or large columns interrupt desk rows and meeting rooms.
• Depth from windows to core: very deep space can leave dark interior zones, while very shallow space limits layout choices.
• Irregular shapes: angled walls and narrow wings create areas that are hard to use.
• Window mullion spacing: this sets the practical widths of perimeter offices and rooms.
• Existing construction: a layout inherited from a previous tenant may waste space for your purposes.

The reliable way to find out how many people a suite holds is a test fit, a quick layout drawn by an architect showing your desks, rooms and support spaces in that specific suite. Comparing test fits across buildings tells you far more than comparing square footage.

The goal is to convert every option to the same basis, so that differences in measurement and efficiency do not hide in the quoted rate.

1. Ask each landlord for both the rentable and the usable area of the suite, and the load factor applied.
2. Ask which measurement standard and edition the building uses.
3. Calculate the total annual cost for each suite, including rent and estimated operating expenses and taxes.
4. Divide that total by usable square feet to get a cost per usable square foot.
5. Have a test fit prepared for the leading options, and divide the total cost by the number of people each layout seats.
6. Note what the common areas include in each building, and whether those amenities replace something you would otherwise build inside your suite.

Cost per person is usually the most meaningful figure for a growing technology team, since headcount is what you are planning around.

• ✓What are the rentable and usable areas of this suite?
• ✓What load factor is applied, and is it the same on every floor?
• ✓Which measurement standard was used?
• ✓Can the landlord remeasure during the term, and can the rent change as a result?
• ✓Does our share of operating expenses use the same rentable area?
• ✓How many people does a test fit show this suite holding?

This normalization is routine work for a tenant representative. When TAG compares proposals for a client, we put each building on a per-usable-foot and per-person basis so the choice does not turn on which landlord measured most generously.