Square Footage Discrepancy

Still, without putting it somewhere on the contract, it was up to you to verify.
It's really quite simple, most actual floorplans are acurate, with a ruler you can come up with the footage and argue for it ahead of time. I did with mine, and with no counter argument against, making a case for my offer per foot on the footage I came up with and we negotiated from there. 10% is not "way" off. (BTW mine was 7% off)

The floor plan is not accurate because they are gaining square footage by counting footage that exists inside the walls. " The physical dimension of each unit consists of the area enclosed by the drywall, including the thickness of such drywalls, located at the exterior wall of the building and the area enclosed horizontally by centerline of any demising walls between the residential unit and the stair and/or elevator and vertically by the upper face of the subfloor of the residential unit up to the unexposed side of sheetrock forming the upper ceiling or the plaster ceiling of the residential unit. " AND THIS IS WHY when people measure their measurements will not correspond with the measurements on the show sheet.

That's just the standard. The size of a space should not be determined by how many walls one decides to put up. Alternatively, you can remove all the walls if you like for a higher square footage. The measurements shown on a floorplan in terms of width and height are typically wall-to-wall, but total square footage includes walls in pretty much everything I've seen.

AND THIS IS WHY you have to allow 10% up and down discrepencies. Just offer LESS per foot.

Tell me, would you rather have 2 extra feet of brick and enjoy peace and quiet, or 2 more feet of air to brag how much less you payed for foot but the wall is so thin your neighbor in the next building can hear your conversation on how shrewd you were?

Point is however, it was on you to establish the footage before going into contract and not relying on a borkers goodwill.

keepwarmnow, whatever happened to measuring the apartment before singning the contract? Buyers need to take some responsibility otherwise overstatements will continue.

This could be the smallest 1724 sq ft apt ever http://streeteasy.com/nyc/sale/580111-condo-441-east-57th-street-sutton-place-new-york
The identicle floor plan here http://streeteasy.com/nyc/sale/430079-condo-441-east-57th-street-sutton-place-new-york is given as 1657 sq ft which is also probably a 300 sq ft exageration.

They're not identical. Each is 1.5 floors, but the half floors are slightly different in size.

The overall sizes seem standard for a 20' x ~72' building with elevator, scissor stairs, trash chute, risers, etc.

I draw floor plans for a living, and do light design work here and there on the side, and In the end most of my clients ask me:
"You've measured my apartment inside and out, now what is my actual square footage?"

I've come across this problem many times, and I would usually tell them 2 numbers.

First number I would give would represent the square footage measured from wall to wall in the inside of the apartment representing the usable square footage. Omitting the interior walls and partitions. for they could be easily moved. This number I believe is fair and a reasonable way to measure the square footage.
However, I've encountered developers that make me include exterior wall thickness into their total square footage. For sometimes joining 2 apartments together, the 6" party wall could add additional 20 sq. ft. and if by some remarkable feat the developer thins out the exterior wall to thin air that 12"-18" could potentially increase the square footage. This number becomes my second number and I tell my clients that this is the size, their property could be considered as. As for marketing upon resale, I leave that up them. So the second number would include the thickness of the exterior walls connecting to the lot line and your neighbors. For technically with a lot of effort you could make that square footage work for you in the future.