Sqf difference between offering plan and net

james, That is a hard question. I will try to answer with a few definitions/assumptions and examples.

Definitions First.

Offering Plan Sq Ft:
Not all condos offering plans measure the square footage the same way. Usually, new condos include the full thickness of non-shared outside walls and 50% of the thickness of shared walls. This is based on ANSI standard for houses but there is no law dictating how the sq footage should be calculated. In some cases, they include a percentage of common spaces (hallways, play room etc) but let us ignore that for this discussion.
Net Square Footage: Sometimes called paint to paint measure means exterior walls are stripped out of the measurement but closets, space taken by plumbing pipes, interior walls etc are included. This is typically what the insurance appraiser of contractor will use for a condo or coop. Net livable area is meaningless concept.

Example 1 (difference on the high side)
Full floor loft. Building size 25x85
Offering Plan Sq Footage: 2125 which includes common stairwell and elevator on your floor.
Net Sq Footage:
Deduction 1.
Assuming exterior walls are 15 inches thick. You need to subtract perimeter 220*1.25= appx 275 sq ft.
Deduction 2: Common Stair well: 7*15 = appx 100 sq ft
Deduction 3: Elevator 6*8 = 50 sq ft
Total Deductions: 425 sq ft.

Net Sq ft: 1700.
Difference 20%.

Example 2 (typical expected difference)
4 condos per floor with each or them a corner condo. Stairs and elevators in the middle. 30x50 condo size including exterior and 50% of shared walls.
Offering Plan: 1500 sq ft in common areas are not included.
Net: Assuming 12 inches thick outside wall and 6 inches separating lobby and apartments.
Deduction 1: 80 x 1 = 80 sq ft for exterior walls.
Deduction 2: 80 x .25 = 20 sq ft for interior shared walls
Deduction 3: Building Structural columns etc: 25 sq ft.
Total deductions: 125 sq ft.
Net: 1375 sq ft. Appx 8-9% difference.

Thanks guys, I was shocked a few years ago to learn that there could be discrepancies in condo square footage. The most common method is to include 100% of non-shared walls and 50% of shared walls. I believe most will include the walls in square footage, but watch out for some that have differing language where their stated square footage is net or just interior square footage.

That can hurt you in later marketing by having to explain this to new buyers ... especially if you bought it on a higher, inflated square footage marketed by the agent.

If you're encountering issues like this, it may make sense to engage an experienced buyer's agent which is free for you to begin with. You can also get a rebate from the buyer broker commission through certain platforms like Hauseit. Good luck and consult a professional!

Your square footage may contain your pro-rata square footage of the building's common elements. So if you have a building heavy with amenities you are going to get a decent amount of square footage added which is not inside your apartment. Let's say you have a building with 10,000 sf of common elements and you have 2% of the common interest in the building: you are gong to get 200 sf added to your unit.

30y, Do lobby and hallways count as common elements? I realize the gym, playroom etc do.

hijacking that question: yes lobby and hallways are common elements (also elevators)

Thanks Ali. I did not realize the extent of overstatement in new condos. I guess I have been lucky in my condo purchases. None of them included any common elements but included exterior walls.

Guys, that's truly shocking to hear that some new developments are including gym etc in their square footage. What about the square footage in the unit's property tax bill online? What does the city use?

This is scary, makes me think you really have to guesstimate yourself or bring in a draftsman before you buy!

Older condos use typically Net SF in offering plan, while newer ones moved to gross SF to have larger sizes.

Check the offering plan as to how they measure and if they use gross SF or net in the schedule A. Or you can check the condo declaration in Acriss for the schedule B and information attached. (free)

From NYT:

Alvin Schein, a Manhattan lawyer who represents condominium conversion sponsors and developers, said condominiums converted in the early 1980's and before used a different technique from condominiums converted or constructed in the past 15 or 20 years.

''When we started doing conversions back in the early 80's, the method for computing square footage of a condo came pretty close to describing the usable square footage in the apartment,'' he said. And the method used by most condos would basically describe the same amount of physical space as the measurement used for co-ops. In other words, back then a 1,200-square-foot condo would have the same amount of usable space as a 1,200-square-foot co-op.

Things are different today, however. ''Somewhere in the mid- to late 80's, someone came up with a way to expand the measurement of a condominium,'' Mr. Schein said. ''Instead of measuring from the inside surface of the walls, they started measuring from the outside face of the walls.''

While that might not at first appear to add significantly to the overall area of an apartment, Mr. Schein said, the additional square footage captured by this method could be significant because of the way some buildings are constructed.

''In some buildings, the exterior walls are 18 inches thick,'' he said, noting that the additional foot and a half could add a significant number of square feet to the final calculation. And that increase would be even greater for corner apartments, which have two exterior walls to account for.

For example, Mr. Schein said, if a corner apartment was 20 feet wide by 40 feet long, and the exterior wall was 18 inches thick, the exterior walls alone would add more than 90 square feet to the apartment's area.

While sponsors and developers generally disclose the method used to calculate the square footage of a condominium apartment, the result often produces confusion.

''First of all, it creates a bit of a distortion because you're including common elements in the measurement of the apartment,'' Mr. Schein said. And second, he said, because the method used has changed over the years, comparing condominium apartments in different buildings may not necessarily be comparing apples with apples. And the distortion can be even greater with larger apartments.

(common elements would be meaning the building exterior walls or interior walls of a hallway or stairway that abut the apartment)

"In other words, back then a 1,200-square-foot condo would have the same amount of usable space as a 1,200-square-foot co-op."

This sounds like drivel to me because there is rarely any official square footage given in Coops. What is listed in Schedule A is room counts. The square footage listed by brokers for Coops is whatever number they make up and is often overstated by extreme amounts.

Great NYT reference, very interesting. So let me ask you this, how does a listing agent approach a condo that he must list that has only net interior sq footage in writing somewhere? What's the best move that's allowable? I realize many listing agents will just make an estimate of the wall size and then list an estimated sq footage