Square Footage of a House – Part 2 of 3

Determining the Square Footage of a House

How Do You Find the Size of a House?

In post 1 (Determining the Square Footage of a House) in this series of 3 posts about how to calculate the square footage of a house, we discussed the most basic aspects of measuring a house. We covered measuring a house that is a simple rectangle without a garage, and illustrated the difference a slight variation in the length of one wall might make when calculating square footage.

In this post, we will review how to measure a house that is slightly more complicated than a basic rectangle. We will also show how to calculate the square footage of a house that is a rectangle plus an additional space.

Finally, we will talk about converted garages and will review spaces that are and are not considered to be living area when determining the size of a home.

Reviewing the Steps for How to Measure a House

The summary of the steps for determining the square footage of a house are:

  1. Measure the exterior of the first story
  2. If the second story (third, etc.) aren’t the same “footprint” as the first floor, measure the interior of the second story, adjusting for thicknesses and open spaces (open staircases, vaulted rooms, etc.)
  3. Remove spaces that don’t count as interior living space
  4. Add it all up

Example 3: A Simple House with a Garage

Garages are not considered to be interior living space, and are therefore not counted as part of the square footage of a house. In an appraisal, garages are still measured, and are clearly marked as being garages, which indicates that they are not living space. A detached garage will still be shown on the property sketch.

For this example, we will show how to calculate the square footage of a house that is a simple rectangle with the garage taking up part of the overall footprint within the rectangle. This type of home can be measured with a long measuring tape and does not require the use of specialized measuring tools.

How to Measure a House - Adding a Garage

The size of this house is 760 square feet.
We obtained this size by first determining the size of the entire footprint of the house (the rectangle) and then subtracting the size of the garage:

25 ft x 40 ft = 1000 square feet

12 feet x 20 feet = 240 square feet (the size of the garage)

1000 square feet – 240 square feet = 760 square feet

Example 4: A Simple House with a Garage and an Addition

This next house looks a lot like the last one, except the owners have built an addition on the back. This addition is 300 square feet (15 feet by 20 feet).

Measuring a House that isn't a Rectangle

Our calculations for the size of this home are almost identical to how we calculated the size of the home in the last example. In this case, however, we added 300 square feet for the size of the addition:

25 ft x 40 ft = 1000 square feet (the largest rectangle)

12 feet x 20 feet = 240 square feet (the size of the garage)

1000 square feet – 240 square feet = 760 square feet

15 feet x 20 feet = 300 square feet (the size of the addition)

760 square feet + 300 square feet = 1060 square feet.

This house has 1060 square feet of interior living space.

In reality, we wouldn’t do it this way. We would use our sketching software to draw the diagram of the house and the software would calculate the dimensions. For a simple house like this, that might sound like overkill. We rarely see a house this simple! Most of the houses we measure have all sorts of angled areas, and bump outs, and stuff that makes calculating the square footage of a house a real headache.

What is Included in the Square Footage of a House?

In addition to the spaces we all recognize are considered to be interior living space, some other spaces are also included:

  • enclosed patios that are heated and air-conditioned and are similar in workmanship (quality) as the original dwelling
  • finished attics – must be conditioned and conforming to the original structure
  • below grade rooms only when typical for the market (e.g.: home on hillside)

What is NOT Included in the Square Footage of a House?

Other common spaces are not considered to be living space and are therefore not included when determining the square footage of a house:

  • screened patios
  • garages
  • unfinished areas
  • 2nd floor airspace (open space, above an entry, or a vaulted room)
  • stairways – open area on 2nd floor
  • basements
  • detached living space – accounted for separately from living space
  • spaces that are accessed only by traversing non-living space, like an enclosed storage area of a garage

These spaces may be determined to add value to the property upon analysis of the comparable properties in an area, but they are not included in the square footage. Some spaces, such as a finished basement, may add value, but at a lesser rate than other finished (above-grade) spaces.

The Converted Garage

We recently received a question about a converted garage that had been enclosed as living space and how converted garages are evaluated when appraising property.

The best answer is, “it depends”.

In order for a converted garage to add value to a property at the same level as the remainder of the home, the converted space must be virtually indistinguishable from the rest of the home. This space must be conditioned space as well – it must be heated and cooled comparably to the rest of the home. Another factor taken into consideration is whether or not other homes in the market area (i.e., the neighborhood, or the area that is considered to have comparable or similar homes) have converted garages. If (unconverted) garages are standard in the area, then even if the converted garage adds some value as living space, the property may also lose some amount of value for not having a garage.

Which way means more $$$$ for the homeowner depends primarily on how the market has treated comparable properties that have recently sold. These properties – the ones that have recently sold – are the ones that tell us, Appraisers, and other real estate professionals such as REALTORS, how the market is treating certain types of properties located within a defined area. Selling fast? Sitting for months? This information impacts the value that will ultimately be determined for a property during the appraisal process.

Converted Garages Example

If an appraiser is appraising a home with a converted garage in a market area of small (1200 square feet) homes where many garages have been converted into conditioned living space, the appraiser will pull the most similar properties that have recently sold (aka, the comps) and will use these market-driven data points to determine the overall value of the property. As long as a reasonable number of comps can be found (at least 3, preferably 6 in our opinion), the garage space will be included in the square footage of the property and no adjustments specific to the garage conversion will be made in the analysis.

(An adjustment is when the appraiser adjusts a comparable property by a specific dollar amount to reflect a difference between that property and the property being appraised – such as adding a certain amount of value for an extra bedroom, or hardwood floors, with the adjustment being determined, again, by the value added that is typical for the market area).

Note how much emphasis we place on the market area.

Different market areas value different property attributes. In some areas of the country, pools are highly valued. And in others, like maybe South Dakota where the pool would be frozen over half the year, maybe not so much. In an area of really small homes in a great central location, a converted garage may be valuable additional living space. In a suburban area of 4000 square foot homes, the garage may be more valuable if left as a garage instead of being converted into bedrooms 6 and 7.

Your appraiser needs to know the market area of the home being appraised to be effectively able to weigh the value, or lack of value, that a particular property attribute contributes to the over all determination of value.

This includes determining the value of a converted garage.

Measuring a House with a Detached Garage

Measuring a house with a detached garage is actually a little easier – both the house and the garage are measured separately, and their sizes are calculated separately.

Here is a sketch of a home with a detached garage, along with the calculations from the software we use for determining the size of the home and the garage based on our measurements from visiting the property.


This came from this hand-drawn diagram:
Hand-Drawn House Diagram

What To Expect in the Next House Measuring Post

In the next post, we’ll take it up a notch and show you how to calculate the square footage of a two-story house. After that, it gets messy, FAST. We’ll show you some sample sketches on paper, and the end results of those sketches when they’ve been entered into our sketching software (DaVinci, from Rapid Sketch, which is integrated into a la mode‘s appraisal software).

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Independent Real Estate Appraiser in Austin, Texas: Travis, Williamson, Hays, Bastrop and Caldwell Counties