How is square footage calculated on a home?

The square footage of a home is the amount of living area with walls and ceilings that is above grade. Official square footage of a home is calculated by the towns tax assessor, although different towns have slightly differing methods of calculation, so the same house in two towns might have a different square footage.

One easy way to look at square footage is the actual footprint of the home. The footprint is the dimensions of the house as it sits. If  the dimensions of a ranch are 30' x 50', for example, the house would be 1500 square feet. If you had a colonial for example, (two floors) you can take  those same dimensions and multiply them by two (as in two floors) and your square footage would be 3,000 square feet.

Calculating the square footage of a home is not as easy as  I just made it sound, though. Neither real estate agents nor homeowners should attempt the calculation (at least not if you want a reliable figure). Houses are seldom perfectly square, which is one big reason for the difficulty. Assessors map out the house on a piece of graph paper, calculate all the edges, come up with "mini-areas" for each rectangle - then add them all together.

Further variables come into play when there is an addition on one floor, an overhang, an enclosed porch, and anything other than a rectangular or square foundation.  Parts of your home that are not included in square footage are decks, outside porches, the garage, and the basement, unless it's a walk out and/or at least half of the room is 50% above grade.

When a home's square footage is advertised, the figure usually comes from tax records, although some agents like to add a few square feet to round off the figure, and others add a finished basement into the above grade living area to attract more buyers to a seemingly larger home, both practices which I find unfair to the buyer, and do not practice when I represent sellers homes. I always look up town records for my clients  to find accurate square footage if I have any questions. If you have any questions about a home's actual square footage, the one defiitive source to rely on 99% of the time are the town records located in the tax assessors office.