Measuring area of a condo/townhouse (real estate, condos, how much)

[jonlovet]

Hi,
I recently bought a duplex (condo-townhouse) in union city. I tried to measure the area today. It happened to be like 150sq feet lower than what was advertised.
assuming the house is rectangular, i measured wall to wall distance in length and breadth. I also added area of stairs. 2 walls are shared and 2 others are not. house does not have patio. it has 3 bed and 1.5 bath, so like 3-4 walls within .. I did not add the area of exterior wall. but when it is being shared, how much area is to be added ? neither did I add area of car parking (which is like 100 ft outside house)
the community has 1bed, 2 bed and 3 bed condos. when i looked up at various real estate websites (zillow,redfin,realtor.com), all 3 bed houses show 1154 sq feet. and 2 bed show 888 sq feet. Am i missing anything ?

[NoMoreSnowForMe]

Normally, the square footage is based on usable space. So, you don't measure from wall to wall. You measure from in front of the kitchen cabinets, or in front of the closets, from in front of bathtub and toilet, etc. Basically, walking around space. That's what I was told, anyway. That may explain your discrepancy.

[jonlovet]

thanks Nomoresnowforme.
I read appraisal report. It shows that the sq feet of my house is equal to what was advertised. First floor has smaller area and second floor has larger. 2 rectangles stack one on top of other. I did not measure the 2nd floor area and just multiplied the first floor area by 2.