How to Calculate Square Footage of a House

By Austin Kilham · July 03, 2023 · 7 minute read

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How to Calculate Square Footage of a House

You’ve likely heard that the most important aspect of real estate is “location, location, location.” If that’s true, then the second most important consideration may be size or square footage.

At its most basic, square footage tells you the size of a property. It can also determine whether you’ll be able to squeeze a king-size bed plus your home office into the primary bedroom or your beloved baby grand piano in the family room.

Square footage also plays a major role in how a home that is for sale is priced. Getting square footage wrong when you are buying or selling can be a big headache and an expensive mistake. For instance, you don’t want to pay too much for a home that’s smaller than you thought it was.

Here, you’ll learn more about how square footage is correctly calculated.

Why Measure Square Footage of a House?

Here are some reasons why you may need to know the square footage of a house:

•   When selling a house, square footage plays a big role in determining the asking price.

Real estate agents will look at comps in the neighborhood — houses of similar size and style — that have sold recently to help them gauge demand for this new listing and set a price.

Square footage isn’t the only factor in pricing a home. An agent will also look at things like condition and building materials when determining value.

•   For those who are buying a home, square footage will play a big part in the price. It’s important that buyers verify that the listed square footage is correct so they know they are getting the space they’re paying for.

When you’re securing a mortgage loan, the lender will need to verify square footage as well, to make sure the house is worth the price the buyer and seller have settled on.

Lenders send an appraiser to conduct a real estate appraisal. This looks at the house to spot anything else that will adversely affect the value of the home, such as cracked walls, leaky foundations, and roofs that need repair.

If a lender’s appraiser finds discrepancies in square footage, there may be issues with a mortgage going through. Lenders may be unwilling to underwrite a loan for a house they think is overvalued for its size.

To save time, buyers should consider doing their due diligence and measure square footage before putting in an offer. Because the size of a house helps determine its value, it also influences property tax assessments.

•   You may also need to know the square footage if you want to dispute a high tax assessment or apply for permits to add on to your house.

Homeowners who think their property is overvalued for tax purposes can dispute the assessment. Confirming square footage is a good place to start. If a home is actually smaller than the recorded size, that may put a homeowner in a favorable position to have their property taxes reduced.

There are a number of reasons the assessed size of your home could be off. Assessors may have used an estimate for their initial assessment, builders may have made a calculation error when they were filing for building permits, or a portion of the house in the initial plans may never have been finished.

If you think the square footage in the public record isn’t correct, contact your city’s assessment department and ask for a review. The city may ask you to file an appeal or a grievance.

Finally, if you’re planning on hiring someone to remodel your home or put on an addition, you may need to know your square footage in order to pull a building permit for the work you want to do.

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How to Measure Square Footage

There are no hard and fast rules about what parts of your house should be included in a square footage measurement.

The American National Standards Institute provides the generally accepted guidelines about how to calculate square footage, but there are no laws governing the issue, and standards may vary by region or even by listing agent. These discrepancies are another good reason to double-check square footage yourself.

That said, the gross living area is what most people mean when they discuss square footage. Here’s an easy way to calculate it yourself.

•   First, get prepared to brush off your drawing skills, and bust out a pen and paper — preferably graph paper. Each square of the graph paper can represent one square foot.

•   Next, moving one room at a time, measure the walls with a tape measure or laser measure, rounding to the nearest half-linear foot. As you measure each wall, draw it out on your paper and write the measurement next to the line.

•   For regular rectangular rooms, you will be able to calculate the square footage by multiplying the length of the room by its width.

•   If the room you are measuring is an irregular shape, break it down into small rectangles, triangles, or other shapes and measure those separately. Add up the square footage of these small areas to get the room total.

•   Add on to your floor plan room by room, and don’t forget to include hallways and closet spaces that may be between rooms. Stairways are also usually counted in gross living area.

•   Do this for every floor of the house, and once you have a complete floor plan, tally the square footage of all the rooms in the house to get total square footage. Round the result to the nearest square foot.

•   If you have a two-story house, you may be tempted to simply measure the square footage of one floor and multiply that by two. The danger with this approach is that not every floor will have the same footage.

For example, if you have any double-height rooms, you can’t count that square footage as part of the second floor.

Note: ANSI guidelines measure square footage from the exterior of the house. This method does not subtract interior walls from the square footage, so it may not give a completely accurate sense of a home’s living space.

Recommended: Things to Budget for After Buying a House

What to Leave Out

Living space that is above the land line and has heating, lighting, and ventilation is included in the gross living area. Garage space does not make the cut. In general, neither do basements, even if they’re finished (although appraisers will include the space in their appraisal valuation).

A good rule of thumb is that anything that is built below grade, i.e. underground, does not count toward gross living area. Other buildings, including guesthouses and pool houses, that require you to go outside to them can’t be included in the gross living area either.

Finished attic space may be included in the gross living area as long as it has enough clearance — generally a ceiling of at least seven feet. Enclosed porches can be included if they are heated by the same unit that heats the rest of the house.

That said, it can be helpful to measure the square footage of these areas for your records, and they can be included separately in a sales listing

💡 Recommended: First-Time Homeowner Guide

Other Considerations Before Buying

If you’re in the market for a new home, the first thing you can do to verify square footage is take a look at the city’s building department records.

When homes or condominiums are built, plans submitted for a building permit include square footage.

Many of these records are available online and provide a way to check whether the listed square footage is at least in the ballpark of city records.

Note that houses that have unpermitted additions will not have that extra space show up in official records.

In fact, add-ons built without going through the proper city channels can add uncertainty to the real estate process, and may not even be included in the gross living area advertised in a real estate listing. And appraisers may not include these additions in the value of the home.

If it’s hard for you to get information on the home you’re interested in from the city and you don’t have the opportunity to measure the home yourself, you can hire an appraiser who can do the measuring for you.

Real estate agents also have a lot of experience determining the square footage of houses. They can give a quick estimate of size or help you measure the square footage more carefully.

There is a lot to think about when buying a house, and square footage is just one factor. There are other things to consider when buying a home.

Would you prefer a smaller house in tip-top condition or a larger one that needs some TLC? Do you like the design and layout or would you be looking at major renovation work to have it be your dream home? Is the location right? Is it near schools, your work, businesses you like to go to, or parks? Is it in your price range?

Recommended: Housing Market Trends by Location

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