Correctly measuring square feet has been a problem for nonprofessionsals for years resulting in some cases serious legal risks. Tax audit reports are for the most part accurate however, if you want to check for your self here are some guidelines.
Measure the House
1. Starting at an exterior corner, measure the length of all walls. Round measurements to the nearest inch.
2. Make a sketch of the home's perimeter, recording all dimensions.
3. If you must measure some areas from inside, add six inches for an exterior wall and four inches for an interior wall.
Determine Finished Living Areas
l Must be space intended for human occupancy.
l Must be heated by a conventional, permanent heating system.
l Must have walls, floors and ceilings of materials generally accepted for interior construction.
l Must be directly accessible from another finished area. That means a finished room accessed through any unfinished space cannot be counted as finished square feet.
Rooms With Sloped Ceilings
Such as the loft found in an A-Frame home. If you measure room dimensions where the sloped walls meet the floor, you are including space that isn't truly usable.
Include only the portion of the room where ceiling height is at least five feet. To be included at all, a minimum of one half of the finished area of the room must have ceilings at least seven feet high.
The area occupied by a bay window may be counted if it has a floor, a ceiling height of at least seven feet, and meets other criteria for living area.
If the furnace, water heater, or other similar item is located in a small closet within the living area, it should be included in the total square footage.
Hallways & Closets
These areas are counted if they are a functional part of the living space.
In general, if the opening for the stairway is larger than its length and width, you must deduct the excess open space from the upper level's square footage.
Open Foyer & Other Open Space
Do not include open space as part of the square footage for an upper level. This may seem obvious, but you'd be surprised how many agents forget to deduct it.