A common question among home buyers is what is included in "Square Feet" measurements. I'll explain what a home appraiser explained to me, and add my own thoughts that you ought to be aware of when comparing homes.
First, no outdoor space of any kind is included in Square Feet (SqFT) measurements. That includes decks, yards, roof decks, etc. Of course each of these add greatly to value. Imagine a deck right off your kitchen allowing you to BBQ or just relax right outside. Two condos with 1,200 SqFt would justifiably feel much different in size, so when comparing Price Per SqFt be careful to take this into consideration.
Second, I was told appraisers measure from the outside of the walls in, and include ALL interior space. This means closets are included, and it of course means an extra wide hallway that can only be used as a hallway, and foyer's or other types of "wasted" space are included. This is VERY important too. The same 1,200 SqFt Condos would have dramatically different living spaces. In many older Victorian or Edwardian Condos you'll find very wide hallways. Whereas in new Condos, or even in other Victorians, you'll find minimal hallway space. I've seen 1,600 SqFt Condos that felt smaller than well laid out 1,200 SqFt Condos.
Lastly, it is not unusual to see significant differences in SqFt measurements. One appraiser might measure from the outside of the wall inward. This adds about 1 foot of space if the walls are 6 inches thick. And then there are just plain old mistakes made in measurements. So as a Real Estate Agent who does VERY thorough "CMA's" (Comparative Market Analysis) to help my Buyers and Sellers understand the value of homes, I DO use price per SqFt to make comparisons. But it is only one of the many things I compare and analyze. I'll try to visit the comparable homes, but when I can't I thoroughly review the photos from the Listing, I read the marketing and "agent-only" remarks, I check the tax records for SqFt size, and I'll call both the Seller's agent and the Buyer's agent in the transaction for the comparable home that sold. After gathering and analyzing all of this information, only then will I be able to include or eliminate some of the ones that seemed comparable based on SqFt size.
The bottom line for you.... as long as the space is livable, and what you want, that should be much more important than a home that claims to be larger, yet doesn't feel it.