Art is 1/2 correct, square footage is but one of many factors that typically correlate to sale price. However it is not irrelevant. We value properties using multiple linear regression analysis and there is always a strong correlation between above ground square footage and sale price.

Whether you use the tax assessors numbers or add up the rooms and multiply by 1.3 (a fair estimate) their will be inconsistencies. This is why you need a large data sample; making a one to one comparison will be highly vulnerable to false correlations.

George,
Most homes listed in the MLS for Wilmette don't even include the square footage. Condition, location, lot size and age are more important and make comparing homes on the basis of square footage a waste of time. Find a home you like based on these other criteria and you'll be much happier in the end.

Calculating the square footage of a home is not an exact science. Usually the tax assessors office with have the square footage but many times it is not accurate do to additions and floor plan changes. Some will take the room sizes and factor in a formula to come up with square footage. Some will measure from the outside walls to get square footage. This method will include hallways and staircases. More detailed methods will remove the non living spaces Square footage is usually the livable space that is heated by conventional methods, finished space and above ground living. Basements usually don't factor in to the square footage.

To get a ball park idea, measure all the rooms and multiply each each room length x width to get the square footage of each room. Add all the room sizes together then multiply by 1.3. This will factor in the spaces such as halls and bathrooms. The result will give you the approximate square footage.