Understanding the Common Area Factor: Rentable vs Useable Square Feet

by CoyDavidson on February 26, 2010

Why do you pay rent for more space than you occupy?

Few commercial real estate concepts are as misunderstood by tenants and even real estate professionals, as the measurement of office space square footage for rent purposes. The formula to determine the amount of rent in most office leases incorporates both the usable square footage, plus the tenant’s proportionate share of common areas in the building.

Useable Square Feet

In general, usable square footage is the amount of space you actually inhabit. For smaller tenants, useable square footage is simply the area of the demised space inside your office suite with no exclusions for recess entry/exit doors or structural columns. What that means in essence, is that the space is measured as if columns are not there. But restrooms and janitor closets, elevator lobbies and public corridors are there, and you pay a portion of the space they occupy with the other tenants who use them.

For full floor or multi-floor tenants, useable square footage is everything inside the glass line, including restrooms, janitor closets or mechanical and electrical rooms. Like small tenants, full-floor or multi-floor tenants also must pay a share of the building common areas not on their floor, such as the main building lobby.

The Common Area Factor

The common area factor is a number which refers to shared spaces on a single floor, and within a building in its entirety. These spaces as previously mentioned can be a pro-rata share of tenant common areas such as restrooms and elevator lobbies, or main building lobbies and amenities which all tenants of the building use.

The Floor Common Area Factor refers to tenant common areas on that floor only, and although the number varies from building to building, it is generally near eight percent of the floor for a factor of 1.08.

The Building Common Area Factor refers to common areas for all the tenants in the building, and can range from six to eight percent. Common area factors determine the actual square footage for which a tenant will pay rent.

Typically when you are quoted a common area factor by the landlord or the building’s leasing agent it includes the sum of the floor common area factor and the buildings common are factor. As a result for most office buildings the total common area factor ranges from 12 to 20% subject to the design of the building.

Rentable Square Feet

Simply stated, rentable square footage is the area of the enclosed interior space of the building other than holes in the floor, such as stairwells, and elevator and mechanical duct space. If it’s floor that you can stand on, you pay for it, because it is rentable space. That includes restrooms, janitor closets, electrical and telephone rooms, etc. What you pay for then-your rent–is the rentable square footage times the lease rate per square foot.

To calculate rentable square footage for a smaller (less than full-floor) tenant, first multiply the usable square footage by the floor common factor, then multiply that result by the building common factor.

Similarly, a full- or multi-floor tenant would multiply its full-floor usable by the building common factor because of the extra shared amenities and lobby space.

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The Calculation

The formulas to determine the usf and the rsf are: rsf = usf x (1 + Add-on %)

Add-On % = (rentable sf / usable sf  –  1)

For example: Assume you need 10,000 usf and there is a 15% add-on factor.

rsf = 10,000 x (1 + .15) = 11,500 rsf

For example: Assume you a leasing 16,000 rsf and have 14,000 usf.

Add-On % = (16,000 / 14,000) – 1 = 14.29%

In some real estate markets a load or common area factor (CAF) is used instead of using an Add-On or Loss factor. Sometimes various landlords have differing definitions of these terms. It is a good practice to always clarify the calculation with the landlord or his agent to ensure there are no misunderstandings.

It is very important for a tenant address this issue before a lease is signed, as there is usually little or no recourse after lease execution. Most leases do not detail a method of direct calculations of either usable or rentable square footage, and if a rentable figure is provided, it is almost always modified with the word “approximate.” However, most reasonable landlords will accept a revision to lease language that the measurement of the premises will be verified by either the tenant’s or landlord’s architect subject to an acceptable measurement standard such as the BOMA Standard or the commonly accepted standard for the market. Your tenant representative should verify that the common area factor represented by the landlord approaches reality.

Comparing Various Buildings

When you are out evaluating space options it is important to note that most buildings have different common area factors and floor plate dimensions or shape can impact the space plan and the required amount of useable square footage. When comparing buildings particularly from a financial aspect you should be using a cost per useable square foot (USF) metric, to be sure you are evaluating your options on” apples to apples” basis.

Ultimately you are looking for the right space that not only fits your budget but also other real estate and workplace criteria. However, two buildings with the exact same face rental rate can have significantly different economic as a result of common area factors and space design efficiencies.

Working with a tenant representation specialist who understand all the intricacies of leasing office space and possesses the technical skills to evaluate various options will insure you are making an informed decision.

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Andrew Zezas, SIOR July 4, 2010 at 4:00 pm


As always, your article is detailed and accurate. One more point worth mentioning is that, in recent years, common area factors have been inflated to become little more than additional profit opportunities for landlords. When that occurs, it has the impact on tenants of inflating actual occupancy costs.

Keep up the great work!

Andy Zezas, SIOR
Real Estate Strategies Corporation – New Jersey

claude September 8, 2010 at 2:34 pm

Thank you for this!

Very helpful!

CoyDavidson September 8, 2010 at 4:31 pm

Claude, glad you found the article helpful. By a landslide this has been the most viewed post on my blog.

Chris Werely January 25, 2011 at 1:06 pm


Great article. Your readers may find these additional articles helpful in regards to space measurement:

Measurement of Square Footage – http://www.kbalease.com/2009/11/measurement-of-square-footage/

Methods of Building Measurement – http://www.kbalease.com/2009/12/methods-of-building-measurement/

Keep up the good work.

Chris Werely
KBA Lease Services & Visual Lease

Birmingham Architects December 9, 2011 at 6:19 am

great article and very helpful. It is important for all property professionals to understand the common area factor. This includes architects who are of course responsible for designing the buildings.

condo in philippines May 25, 2012 at 4:10 am

Agree it is important to know the area of space usable for leasing purposes. Not only for property professionals, tenants must be aware of the common area of space they are leasing on a certain property. 

JJInfra June 7, 2012 at 12:37 am

Great post !

Mary June 11, 2012 at 1:37 pm

what is the maximum allowed load factor can landlord charge for a highrise office building in california

Coy Davidson June 11, 2012 at 10:22 pm

While I don’t practice in California, if it is like Texas the building owner can charge whatever the market allows. You won’t see a building owner apply a load factor more than the actual factor, as that would be considered deceptive, but in many cases the building owner will apply a load factor less than the actual common area factor for marketing purposes.

Thomas April 23, 2013 at 11:30 am

You mention common area factor, would i be right in thinking that it can vary considerably by building. A single story building will have a
lower add-on or common area factor than a multi story building. A 15%
add-on factor for a typical multi story building is not unreasonable,
but low 20% is not unheard of.

Coy Davidson April 23, 2013 at 2:09 pm

Thomas, yes you are correct it does vary from building to building and its but its not always the number of floors but the design or size of the common areas. Also if you lease an entire floor it is typical that the common area factor is less for a floor with multiple tenants.

Connie June 19, 2013 at 6:57 am

I have a question, I rent a town home there are 50 units and the land lord told us that our front yards are common area?? have you heard of this before? If so what does that mean??

CoyDavidson June 24, 2013 at 5:34 am

Common areas are available for use by all tenants in the property. This means all 50 tenants or users have rights to use any area of the real property that is deemed common areas, such as the lobby of a building or in this case the front yards. This is not unusual.

Oliver Finney June 29, 2013 at 4:42 am

Very insightful. I thought getting property reports is just enough to make well-informed decisions on buying or selling or renting a property. I didn’t know you can actually calculate the real value of the space. Thanks very much!

Bill July 14, 2013 at 7:06 am

Thanks for a very informative and helpful article. For a full-floor user of a first floor with a corridor from the building entrance to the elevators, would the corridor be included in rentable square feet It is “inside the glass,” but clearly used by all tenants. Thank you.

KIM August 27, 2013 at 7:17 pm


Bethany September 25, 2013 at 10:38 am

I have a commercial lease. The rentable square feet featured in the lease is 180 more than the amount of floor space I actually have access to. That space seems to be inside the walls, the landlord has referenced BOMA in his justification of including that space in my rent. I am wondering if this is common practice. I have not yet begun paying rent.

t@yahoo.com October 8, 2013 at 3:46 pm


Brett Haynes February 5, 2014 at 9:26 am

Well presented and to the point. With the exception of a handful of buildings in our market we don’t end up dealing with this in leases. But, it is certainly important information to know.

Ravi April 8, 2014 at 12:44 pm

Can a Landloard charge a tenant for the Elevators as usable sq.ft. For example, the elevators only stops and can be accessed on 5th to 10th floor. A single tenant happens to fully occupy 5th to 10th floor and blocks the public access to these elevators on the ground floor so no one can get to the lobby without passing the security point.

Coy Davidson May 6, 2014 at 5:25 pm

Ravi ,typically vertical penetrations ie elevator shafts are not included in the calculation. However, it depends on how the lease reads. If the lease does not spell out a standard of how space is measured, then theoretically they could. You might refer to this document; https://www.dropbox.com/s/tflfof5nwgofk38/ANSI_Standards_202723_7.pdf

Bill McInerney May 29, 2014 at 3:16 pm

Good post. I come from the school and my first rule is, “always measure” leased space. Never take anything for granted. Then always check on the actual building size via city or town hall records.
Bill McInerney

KD July 1, 2014 at 1:50 pm

We rent a small office on a floor in a large building. The floor we are on otherwise unoccupied (all other tenants have moved out). We measured our usuable space (the actual space we occupy) in order to re-arrange the office space and we have come to find out the square footable is approximately 200sf less than what we have been paying for listed under “Occupant Area”. It is approximately 350sf less than the “Rentable Area” which includes a conference room that is not maintained by management therefore the room is filthy, full of magazines stored there by a tenant who no longer occupies space in the building, used and moldy coffee machines, and garbage. We are going ROUNDS with our landlord as our lease is up and we’d like to avoid moving but feel we are paying for space that is not usuable (I do understand common areas such as usage of the elevator, and restrooms, but those do not equal our leased SF in either category). What else can I do?

Jim November 10, 2014 at 3:38 pm

Is it common practice for a building to have a “load factor” for common area share (say 13%) as well as CAM charge of $.09/sf.

Coy Davidson November 10, 2014 at 6:45 pm

Jim, yes it common practice. The load / common area factor and CAM are two different issues. Common area factors area way for the Landlord to charge rent for the common areas of the building on a pro-rats share. CAM charges are for the building operating expenses.

Keilon George December 4, 2014 at 5:09 pm

Great Post Coy!

Matt December 14, 2014 at 1:37 pm

We are constructing a building that will have two prominent decks on each floor. These areas will be covered and very useful but clearly “outside”. The tenants will be whole floor so these decks will not be “common.” How should I value this square footage in lease terms? Is there a rule-of-thumb discount for such space?

ted December 17, 2014 at 9:43 am

The article, the questions and the answers were all very informative, thank you to everyone and Coy.
I just wished listings always included some information on CAM expectations.

Chip March 23, 2015 at 6:16 am

I am working with a tenant leasing 3000SF on the first floor of a 2 story building. Each floor is 25,000 SF. The first floor has a large lobby including the elevator to the 2nd floor. How do I calculate the R/U factor on the first floor as the large lobby also accommodates the 2nd floor tenant? Thanks

Brian April 15, 2015 at 8:38 pm

Looking to lease a retail property. Would you recommend to quote the rent according to usable area or rentable area?

CoyDavidson April 18, 2015 at 9:30 am

Typically retail space does not have a common area factor, this typically applies to office space.

jacquline isom September 5, 2015 at 7:46 am

we rent a small office space but are wanting to expand well the landlord is wanting to charge us extra to move a partition wall about 5 ft in order for us to be able to securely lock our space from other renters and inside that 5ft move is a open elevator shaft not in use we have ask them to close it off for the safety of our customers and they dont want to do that what can we do about this

Rick September 29, 2015 at 7:02 pm

Hello Coy –
Good post. Question: Do you have thoughts on the potential of a “capped load factor” at the discretion of the landlord, as provided by the BOMA calculation, relative to compliance issues (Stark, etc.), when the landlord is a hospital and the tenant is a physician group? Thanks……Rick

Coy Davidson September 29, 2015 at 10:57 pm

I never heard of such a thing s the common area factor tied to Stark compliance issues.

Tammy Buhler February 7, 2016 at 6:20 am

Question: i broke my ankle a year ago & now my landlord took my crutches & my cast (it’s a boot w/ velcro straps to keep the foot straight) from outside my bdrm door and locked them up saying that she placed them in a ‘safe place’ cause they were in the ‘common area’ according to her…she doesn’t have any legal right to do so, does she?

CoyDavidson February 8, 2016 at 7:30 am

Tammy, this is really a legal question. My article is related to the common area for a commercial office building.

Jacqueline Alexander Reece April 25, 2016 at 9:29 pm

I have a commercial lease from TX and we have NRSF fees and they total 130.00 monthly throughout the lease from 2011 I signed the management has never utilized this fee, my lease expires in Aug 2016, they have tried to enforce the fee since Jan 2016 but they sent the notice by email which I just notice and says we have cumulated back pay of 400$ when asked management said they wanted to get me to sign a new lease, on the new lease these fees “nsf” would increase annually should I run now or try to work this out?

Anil Kumar September 3, 2016 at 3:38 am

I am planning to buy a flat in a High raise towers gated community.
The area of flat as per sale deed is 1842 square feet and when measured the flat, actual is 1175 square feet.
The builder says the rest is common area. It is working out to 36%.
Is there any rules controlling the common area charged by builders?
36% common area charging seems too high.
Please advise.

Benny December 5, 2016 at 11:20 am

Is it legal in Florida to charge 40% instead of the 12-20 common area addition? Is there a legal remedy if the building that I have been renting from add 40% for the common space? Please help..

Tracy Battagler Stanley February 2, 2017 at 7:33 pm

Im so pissed at the moment and need advice. We have lived in a Apartment for 4 years and there are only 6 units. Two in basement, two on main level, and two upstairs. We are on main level and this is the fifth time of having new neighbors in the unit acrossed from ours. There is a space that leads to our apt with some storage but we have never been told nor shared it with other tenants. The door into that area is a small area with a storage closet then our door into our apt. It leads no where but to our apt. No one has any reason to even come in that area. Now we are being told that its a commonly shared space with the tenants next door. The closest is large but not divided in anyway for separate use. Again that area is one door you open it and there is the storage and another door that goes into our apt thats it. So my question is if its not in our lease or we never been told it was a common area do we have to share the space? Sorry for rant just upset. Advice anyone???

Muhammad Rizwan April 3, 2017 at 5:23 am

Charging for common space has to be pro-rated to your apartment. i.e. 1,842sqf divided by the total area of your entire floor yields the weight of your apartment, then multiplied this weight by the rental cost of that 36% common area, result will be your cost of using those common areas, in addition to the rent you’d be paying for your apartment.

Deanna Bagby April 6, 2017 at 1:33 pm

Does your lease agreement list square footage? If so see if the square footage of the storage space is included.
If not is there a mention in the agreement about the storage space. That’s where I would start.

Deanna Bagby April 6, 2017 at 1:37 pm

I would check comparable properties to see what they list. But like Muhammad stated the common area space is pro-rated.

RGII April 27, 2017 at 3:03 pm

I know this is old as can be but it’s still relevant.

As a large office developer I can attest to the constant complaints about useable vs rentable sf. We cap our core factor at 15% even if our building ends up with an 18% core factor.

We put one of our office buildings in a condominium and one of the first floor tenants always complains about the condominium dues because he doesn’t use the elevators or the first and second floor common areas. I always tell him that his space is worth $250/sf because he’s in a three story class A building. If he wanted no elevator and no second/third floor to pay for then he could have bought in a strip mall.

Andrea McCarthy July 19, 2017 at 10:26 pm

I think your definitions of each of these terms are very clear and concise! I also agree with you that addressing the RSF and how it is determined is important before a lease is signed. Great article!

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