How Much Space Are You Selling?

Every year, incorrectly measured square footage results in numerous lawsuits against sellers and real-estate agents. If you are working with a real-estate agent, it's the agent's responsibility to get the correct square footage number; FSBO sellers must make sure to do this themselves.

It's critical to understand how residential living space is calculated. Never depend on the square footage statements found on a previous multiple listing sheet or county tax records. You can't use blueprints to figure square footage, because last-minute changes might have been made during the home's construction. Don't use appraisals, either, because even appraisers make mistakes. Your reputation and finances are both on the line, so measure square footage yourself using accepted techniques, then cross check the results with previous calculations, if they are available.

It's a good idea to calculate a home's total square footage, which includes finished and unfinished spaces, and even the area occupied by decks and patios. You never know when a prospective buyer will want both figures, so be prepared to answer their questions before you advertise the property.

Your state's real-estate commission might have already established square footage guidelines that you can follow. Call your state real-estate commission or look on its Web site to determine if measuring standards are in place.

The methods described here are based on widely accepted square footage guidelines, so they will help you learn the basic do's and don'ts of calculating residential square footage. No matter which measuring method you decide to use, hang on to your drawings and all other paperwork associated with the procedures you used to measure the residence. You'll be in a much better position to defend your calculations if you can show how the results were obtained.

Measure the Exterior

Square footage calculations are always based on exterior measurements. Use the following techniques to measure the exterior of a single-family residence:

  • Start measuring at one corner of the house and continue to measure the remaining exterior walls. Round measurements up to the next inch (or tenth of an inch for greater accuracy).

  • Record your measurements, and use them to make a sketch of the perimeter of the house.

  • Sketch in the position of unfinished areas, such as garages and utility areas.

  • If all areas of the structure qualify as living areas, you will use your sketch and measurements to calculate the square footage of the entire shape.

Sometimes you must determine a portion of a home's dimensions by measuring from the interior. When that happens, add six inches for each exterior wall and four inches for each interior wall you encounter during the measuring process and then sketch the area in to your exterior drawing.

What qualifies as finished living space?

Finished square footage must be space intended for human occupancy. It must be heated by a conventional, permanent heating system. It must be finished, with walls, floors, and ceilings that are constructed from materials generally accepted for interior construction. It must also be directly accessible from another portion of the living area.

Unfinished areas must be deducted from the total square footage. Garages and unfinished utility areas are examples of rooms that must often be subtracted to obtain the total for the living space. Sketch them in, and deduct their square footage when you make calculations.

Other Measurements

If you've got sloped ceilings, as in A-frame homes or in the attic where ceilings are usually sloped at a sharp angle, you can't just measure room dimensions where sloped walls meet the floor. Include only the square footage for the portion of the room where the 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.

Bay Windows

The area occupied by a bay window may be counted in your total square footage if it has a floor, a ceiling height of at least seven feet, and meets other criteria for finished living area.

Furnace Rooms

If the furnace, water heater, or other similar item is located in a small closet within the living area, the area should be included in the total square footage.

Hallways and Closets

Hallways and closets are counted as part of the total square footage if they are a functional part of the living space. For instance, they are included if they are in a bedroom or within another room that's heated and finished. A closet in an unfinished basement should not be counted.


If the upper 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 Foyers and Other Open Spaces

Be careful not to include open areas on the first level as part of the square footage for a home's upper level. This may seem obvious, but you'd be surprised how many people forget to deduct that space when totaling their figures.

Rooms Accessed Through an Unfinished Area

You should not count the square footage of a room that is finished and heated if it is accessed through an unfinished area — for instance, a laundry room that you enter by walking through an unfinished basement or garage. You can describe the space in your advertising, but be sure to mention that it is not included in the home's square footage.

Commonly Used Mathematical Formulas

You'll encounter several common shapes when you measure a home's square footage, and the area of each shape is calculated using a specific formula. Here are several formulas and graphics that will help you complete your square footage calculations.

Rectangles and Squares

Calculating the area of rectangles is easy. All you need to do multiply length by width. For example, if a room is ten feet in length and eight feet in width, the area is eighty square feet.

A = L × W


If you've got a triangular area to measure, figure out the length of the base and the height, then multiply the two figures and divide the result in half. For example, if the base is ten feet and the height is fifteen feet, you'll need to do the following calculations: 10 × 15 ÷ 2 = 75.

A = B × H ÷ 2

Circles and Semicircles

To calculate a circular area, you'll need to calculate the radius (the distance from anywhere in the circle to the center), square the result, and multiply it by Π (roughly 3.14). For a circle with a ten-foot radius, you'll need to do the following: 3.14 × 102 = 314 square feet.

A = π × R2

If you have half of a circle, divide that number by two. If you have a quarter of a circle, divide the total by four.

Take a second look at your sketch before you leave the house, making corrections if necessary. Once you are accustomed to doing it, measuring square footage isn't difficult at all.

Combined Shapes

If you've got oddly shaped spaces, try to break them down into simple geometric figures like rectangles and triangles, then calculate the smaller areas and add them up.

Break down complicated shapes into rectangles and triangles.

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