How to Accurately Calculate Square Footage of a House

Understanding how to calculate the square footage of a house is key when you’re buying, selling, or renovating a home. Square footage determines property value, tax assessments, and even how much flooring or paint you need. 

But measuring a home’s size isn’t always as simple as it seems. Some areas count toward total square footage, while others, like garages and unfinished basements, may not. For example, in cities like San Francisco and Chicago, local building codes can influence what counts as livable space. 

This Redfin guide will walk you through how to measure square footage accurately, what is and isn’t included, and answer common questions, like “Is a garage included in square footage?”

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Square footage is most commonly measured using standards set by the American National Standards Institute (ANSI). These guidelines offer a consistent method for determining a home’s size by focusing on finished, livable space and using the home’s exterior dimensions.

Here’s what ANSI requires when calculating square footage:

• Measure from the exterior: Square footage is calculated by measuring the outside walls of each level. Wall thickness is included in the total but not subtracted.
• Only finished, above-grade spaces count: Finished areas must be heated, permanently enclosed, located above ground level, and accessible from the main house.
• Measure each level separately: For multi-story homes, the finished area of each floor is measured on its own and then added together.
• Ceiling height matters: To be included, spaces must have a ceiling height of at least 7 feet, or 6 feet 4 inches in areas under beams or sloped ceilings.
• Exclude non-livable spaces: Garages, unfinished attics or basements, and areas not directly connected to the main living space aren’t counted. Finished basements are usually noted separately but aren’t included in the official square footage under ANSI standards.

Check local guidelines 

While ANSI guidelines are widely used, definitions of “livable square footage” can vary by location. Some cities, like Los Angeles, exclude spaces like balconies or garages unless fully finished. In NYC, strict building codes may disqualify rooms without proper windows or ceiling height. Seattle’s zoning laws can also affect whether lofts or upper rooms count. Always check local regulations, especially when listing or appraising a home.

Before you break out the tape measure, it’s important to understand what “square footage” actually includes because not every part of a house counts toward its total square footage. Under ANSI guidelines, only finished, heated, and above-grade areas are included in a home’s official square footage.

Areas typically included in the square footage of a house:

• Finished, heated rooms (bedrooms, living rooms, kitchens, bathrooms, sunrooms)
• Closets, built-ins, hallways, and other finished interior spaces
• Finished attics that meet ceiling height requirements
• Staircases (counted in the square footage of the floor they descend from)

Areas not typically included in total square footage:

• Garages
• Basements (finished basements are usually not included unless they meet livable space standards)
• Attics or lofts that don’t meet requirements
• Porches, balconies, and decks (unless fully enclosed, heated, and finished to the same standard as the home, they’re excluded)
• Detached structures (guest houses, sheds, ADUs, etc. are not included in the main square footage of a house)
• Storage areas and crawl spaces

Step 1: Divide your home into measurable sections

Instead of trying to measure the entire house in one go, break it into smaller, rectangular sections such as individual rooms, hallways, and closets. This method minimizes errors and makes calculations easier. For non-rectangular rooms (like L-shaped areas), divide them into smaller rectangles and measure each one separately.

Sketching a basic floor plan can be helpful to keep track of your measurements and ensure no areas are missed. It doesn’t need to be perfect – just clear enough to label dimensions and organize your measurements as you go.

Step 2: Measure each room

• Use a tape measure or laser distance measurer.
• Measure the length and width of each room or section from wall to wall, keeping the tape straight and level for accuracy.
• Record each measurement clearly on your floor plan sketch.

Step 3: Calculate square footage of each room

The next step is to calculate the square footage of each space using this formula: 

Sq. feet = Length x Width

• Take the length and width measurements you recorded for each room.
• Multiply the length by the width to get the square footage of that section.
• Repeat this process for every section of the home and note the square footage directly on your sketch.

For example, if a bedroom is 12 feet long and 10 feet wide, the calculation is:

12 x 10 = 120 square feet

Step 4: Add up the square footage to find the total

Once you’ve measured each section, add all the values together to get the home’s total square footage.

Example square footage calculation:

Tips for measuring irregular spaces

If your home isn’t a simple rectangle, here’s how to tackle more complex layouts:

• L-shaped areas:  Break the space into two rectangles. Measure each one separately, then add the totals together.
• Triangular spaces: Measure the base (widest part) and the height. This will help you estimate the overall area.
• Circular areas (like turrets): Measure straight across the center to get the diameter. From there, you can estimate the square footage or consult a professional for more precision.

Measuring multi-story homes

• Measure each floor separately.
• Add up the square footage from all finished levels.
• Don’t include unfinished spaces like attics or basements unless they meet local criteria for livable space.

Measuring open floor plans

• Measure the full length and width of the open area.
• Subtract any spaces that aren’t considered livable.

Why accurate square footage matters

Knowing how to measure square footage correctly is important for:

• Real estate listings: Buyers compare homes based on price per square foot.
• Home appraisals: Square footage affects property value.
• Renovations: Knowing the exact dimensions helps with materials and budgeting.
• Property taxes: Local governments assess taxes based on your home’s square footage.

Square footage plays a critical role in a home’s value, so both buyers and sellers should ensure the number is accurate. Even small discrepancies can impact home pricing, appraisals, and buyer negotiations. Here’s what each party should consider:

For sellers: avoid overstating or understating your home’s size

• Verify, don’t assume: Even if you have builder floor plans, the as-built square footage can differ from the original designs due to changes made during construction. Always measure independently or hire a professional appraiser.
• Avoid pricing pitfalls: Listing your home with incorrect square footage can lead to mispricing, which might scare off buyers if they later find discrepancies during an appraisal or inspection.
• Legal and ethical considerations: Misrepresenting square footage (even unintentionally) could lead to legal disputes or buyer demands for a lower price. Some states have disclosure laws requiring sellers to provide accurate home measurements.

For buyers: don’t rely solely on listing numbers

• Check the measurements: Real estate listings often pull square footage from tax records, which may not be updated or accurate. Ask for recent appraisals or measure the home yourself.
• Know what’s included: Some listings may include non-livable areas like finished basements, sunrooms, or enclosed patios in the total square footage. Confirm what is counted, especially in states where rules differ.
• Appraisal discrepancies can affect financing: If the appraiser measures a lower square footage than what’s listed, it could impact mortgage approval and home value assessments, leading to renegotiations.

FAQs: Calculating the square footage of a house

Is a garage included in square footage?

No, garages are generally not included in a home’s official square footage. Even if attached or finished, garages are considered non-livable space and excluded from ANSI square footage calculations. However, garages may be noted separately in real estate listings.

Do finished basements count toward the total square footage?

Finished basements are typically not included in the official square footage because they are below grade. They may be listed separately as additional finished space, but don’t usually count toward the home’s above-grade total.

In rare cases, if a basement is fully finished, heated, and has proper egress (windows or doors that meet building codes), certain local appraisal or MLS guidelines might count it toward total living space. Always check regional rules to know how basements are treated in your area.

Why does my home’s square footage differ between listings and tax records?

Square footage can vary because tax records, MLS listings, and appraisals may use different measurement standards or may not be updated. Tax records often use rough estimates and can be outdated.

Can I measure the square footage myself?

Yes, you can take your own measurements using the steps in this guide. However, for official purposes like selling or appraising, it’s best to hire a professional who follows ANSI standards.

What’s the difference between gross living area (GLA) and total finished area?

GLA typically refers to finished, above-grade living space measured to ANSI standards. Total finished area may include finished basements or other below-grade spaces but is reported separately.