How does an appraiser calculate square footage?

Every appraiser has their own preferred method of calculating the square footage of a home. Some use a tape measure to carefully take the dimensions of each room, whereas others use a laser device that eliminates manual measuring. For difficult-to-measure spaces, experienced pros may just eyeball it. As a result, different appraisers will often come up with a slightly different square footage of the same home.

Where can I find a good square footage calculator?

You can find lots of reliable square footage calculators online, including examples from Calculator Soup, the Calculator Site or Calculator.net. Many can calculate price per square foot as well.

How do I calculate the square footage of a roof?

To calculate the square footage of a roof, start by measuring the length and width of every roof surface, including dormers. Then, multiply the length and width of each rectangular section of roof to find the area. If there are triangular sections of roof, calculate the area by multiplying the length of the triangle's longest side by its height, and divide by two. The last step is to add up the area of all roof planes to get the total square footage of the roof.

How do I calculate square footage for a triangular room?

You can calculate the square footage of a triangular room by measuring the base of the triangle, which is the length of the longest wall. Then, measure the height to the top of the triangle. Multiply the base and height together, and divide by two to get the square footage of the room.

Are closets included in the square footage of a home?

Closets are often included in the square footage of a home, but not always. Any space inside a home that has walls, a floor, a ceiling and heat are usually counted toward the overall square footage. However, if there are closets that don’t meet the requirements, like in an unheated, unfinished basement, they probably would not be counted.

How to calculate the square footage of a home (and why it’s important)

Written by

Elizabeth Rivelli,

Edited by

Michele Petry

Published on July 07, 2022 | 7 min read

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When you buy a new home, thinking about how to measure its square footage probably isn’t top of mind. And while it may seem like an inconsequential metric, it’s one of the most important factors that determine a property’s value.

“If you mismeasure a property, it’s a domino effect — it’s going to throw the whole value off,” says Marlon Day, senior director of Quest Valuation & Advisors in Atlanta.

Square footage statistics

The median price per square foot for a home in the U.S. is $123, according to data from Realtor.com. However, price per square foot can vary greatly depending on location.
The average size of a home in the U.S. in 2020 was 2,261 square feet, per Statista. Its data shows that home sizes have decreased every year since 2017, when the median was 2,426 square feet.
In 1950, the country’s average home size was 983 square feet, per the International Association of Certified Home Inspectors.
The average bedroom size, according to CRD Design Build, is roughly 132 square feet. There are specific requirements regarding what can be considered a legal bedroom, including required square footage, ceiling height and modes of egress, which vary from state to state.
The U.S. has the highest average number of rooms per person around the world, with 3.8 rooms per household member, according to data from international policy group the Organisation for Economic Cooperation and Development.

Why square footage is important

There are plenty of reasons you might want to know how to calculate the square feet of a house, whether you’re looking to sell a property, dispute a high tax assessment or renovate to add more space.

If you’re preparing to list your home for sale, determining the property’s exact size is a crucial factor when setting your asking price. “For a home appraisal, we’re going to compare it to comparables or ‘comps,’” says Day, who looks for homes of similar size in the immediate area. An inaccurate square footage measurement could potentially result in an inaccurate appraisal price.

Square footage (often abbreviated as SF or SQFT) also matters in real estate deals that involve a mortgage, for similar reasons. The lender will want that info to verify what the property is worth.

However, knowing your home’s square footage can come in handy in other ways as well. For instance, if you decide to finish a previously unused part of your house — say, a basement or attic space — you may need to provide the square footage to obtain a building permit.

Likewise, if your county or municipality assesses higher taxes than what you think you should owe, confirming the square footage can be a point in your favor toward getting the property taxes reduced.

How to calculate the square footage of a house

When preparing to measure the square footage of a home, be it a house, condo, or townhouse, start with a few simple supplies:

Paper and pencil
Calculator
Measuring tape and/or laser measuring tool

If the property is a perfect rectangle, simply measure the length and width and multiply those two numbers together. For example, if your one-story house is 60 feet wide by 40 feet long, then your property is 2,400 square feet (60 x 40 = 2,400).

However, most properties have more complex floor plans. When this is the case, it’s helpful to follow these simple steps to measure square footage.

Draw a rough sketch of your entire space, labeling all of the rooms you need to measure. Include hallways and vestibules as their own “room.”
Measure the length and width, in feet, of each room. Then, multiply the length by the width to calculate that room’s square footage. For example: If a bedroom is 12 feet by 20 feet, it is 240 square feet (12 x 20 = 240). For each room, write the total square footage in the corresponding space on your sketch.
Once each room is measured, add up all the measurements to determine your home’s total square footage.

Note

If you live in a tract home, condo or townhome community, you may be able to get architectural drawings or master builder plans of your floor plan. These may already have your square footage calculated.

What to leave out

A good rule of thumb to ensure you’re taking proper measurements is to exclude space you can’t walk on or live in. These types of spaces do not count as “gross living area.”

“Someone might think, ‘If I get the measurement of my first floor and I have a two-story house, I just multiply that by two,’” Day says. However, if that first floor includes a two-story foyer, you can’t count the non-usable space.

Basements and garages, even if they are finished, don’t generally count toward total square footage. Basements are typically excluded because they are built below grade, meaning below ground level. If your state does allow basements to be included in the total square footage of a home, though, you’ll likely need an ingress and egress, or a safe way to enter and exit the basement to the outside.

Finished attic spaces — with some regulations, including ceiling heights — can count toward the total square footage of your home. If you are planning to sell your home, work with a real estate agent to craft a listing that accurately reflects your property.

When in doubt, ask the pros

If calculating the square feet of your particular property feels overwhelming, consider hiring a professional appraiser to do it. The average appraisal cost for a single-family home typically runs about $350. A condo appraisal fee is generally between $300 and $500, and multi-family home appraisals can run anywhere from $600 to $1,500.

While two different professional appraisers could evaluate the same home and come up with slightly different square footage figures, they do all aim for scientific accuracy. “We’re always shooting for somewhere between 1 to 3 percent variance,” Day says.

FAQs

Every appraiser has their own preferred method of calculating the square footage of a home. Some use a tape measure to carefully take the dimensions of each room, whereas others use a laser device that eliminates manual measuring. For difficult-to-measure spaces, experienced pros may just eyeball it. As a result, different appraisers will often come up with a slightly different square footage of the same home.
There are lots of reliable square footage calculators online, including examples from Calculator Soup, the Calculator Site or Calculator.net. Many can calculate price per square foot as well.
To calculate the square footage of a roof, start by measuring the length and width of every roof surface, including dormers. Then, multiply the length and width of each rectangular section of roof to find the area. If there are triangular sections of roof, calculate the area by multiplying the length of the triangle’s longest side by its height, and divide by two. The last step is to add up the area of all roof planes to get the total square footage of the roof.
You can calculate the square footage of a triangular room by measuring the base of the triangle, which is the length of the longest wall. Then, measure the height to the top of the triangle. Multiply the base and height together, and divide by two to get the square footage of the room.
Closets are often included in the square footage of a home, but not always. Any space inside a home that has walls, a floor, a ceiling and heat are usually counted toward the overall square footage. However, if there are closets that don’t meet the requirements, like in an unheated, unfinished basement, they probably would not be counted.