How to Accurately Calculate Square Footage of a House

Knowing how to calculate the square footage of a house is crucial whether you’re in the market to buy, sell, or renovate a home. Square footage plays a significant role in determining property value, tax assessments, and the amount of flooring or paint needed. However, measuring a home’s size can be more complex than it appears. Some areas count towards total square footage, while others, like garages and unfinished basements, may not. Local building codes in cities such as San Francisco and Chicago can also impact what is considered livable space.

This guide from Redfin will walk you through how to accurately measure square footage and address common questions like whether a garage is included in square footage calculations.

How is the square footage of a house calculated?

Square footage is typically measured following the ANSI (American National Standards Institute) guidelines, which provide a standardized method for calculating home size. The ANSI method involves measuring the exterior dimensions of the house, including all finished, livable spaces.

Here’s how it works:

1. Measure the exterior: Professionals measure from the outside walls to calculate total square footage, including wall thickness in the total.
2. Include finished areas: Any heated, livable space that meets height and accessibility requirements is counted, such as main living areas, bedrooms, bathrooms, and finished attics with at least 7 feet of clearance.
3. Exclude non-livable spaces: Garages, unfinished basements, and areas requiring you to leave the main house are not included in the home’s square footage. Finished basements may be listed separately in real estate listings.
4. Measure each floor separately: For multi-story homes, each level’s livable space is measured and added together to determine the total square footage.

While ANSI guidelines are widely adopted, local real estate markets may have variations in rules. It’s essential to check regional regulations to ensure accurate measurements, especially when listing or appraising a home.

4 simple steps to measure the square footage of your home

Step 1: Gather your tools

To measure a home’s square footage, you’ll need:

• A measuring tape or laser distance measurer
• Pencil and paper (or a digital note-taking app)
• Calculator

A laser measurer can be particularly helpful for larger spaces and provides more precise measurements.

Step 2: Divide your home into measurable sections

Rather than attempting to measure the entire house at once, break it down into smaller, rectangular sections like individual rooms, hallways, and closets. This approach minimizes errors and simplifies calculations. For irregularly shaped rooms (e.g., L-shaped areas), divide them into smaller rectangles and measure separately.

Step 3: Measure each room’s dimensions

For each room or section, follow these steps:

1. Measure the length and width in feet.
2. Multiply the length by the width to obtain the square footage of that section.

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

12 x 10 = 120 square feet

Repeat this process for every section of the house.

Step 4: Add up the square footage

Once you have measured each section, sum up all the values to determine the home’s total square footage.

Example of calculating the total square feet of a house:

What counts towards the square footage of a house?

Square footage generally includes finished, livable spaces within the home. Here’s what is typically included and excluded in official measurements:

Included in square footage of a home:

✅ Finished bedrooms, living rooms, kitchens, and bathrooms
✅ Heated and cooled areas (e.g., central HVAC or permanent heating source)
✅ Finished basements (if they meet livable space standards)
✅ Enclosed sunrooms (if heated and finished)

Not included in square footage of a home:

❌ Is a garage included in square footage? No, garages are not counted in square footage because they are not finished, livable spaces.
❌ Unfinished basements, even if enclosed
❌ Attics or lofts that don’t meet height requirements (typically at least 7 feet high)
❌ Porches, decks, and patios (unless enclosed and heated)

Check local guidelines

If you’re selling a home, it’s important to review local real estate guidelines as definitions of “livable square footage” can vary.

For example, homes in Los Angeles have specific rules for measuring livable space, especially regarding balconies, garages, or basements, which may not be included in the total square footage unless fully finished. NYC has strict building codes that distinguish between “habitable” and “non-habitable” spaces, meaning certain rooms or areas may not count towards the total square footage if they don’t meet specific criteria (e.g., windows or ceiling height). In Seattle, rules around livable square footage may be influenced by zoning laws and building permits, with areas like lofts or small upstairs rooms being counted differently from standard living spaces.

How to measure irregular-shaped homes and spaces

If your home has an irregular shape, there are methods to measure its square footage accurately, though you may need to use different techniques.

L-shaped areas: Divide them into two rectangles, measure separately, and add their square footage.

Triangular spaces: Measure the base and height, then use the formula:

(Base×Height​)/2

Circular areas (like turrets or round rooms): Measure the diameter (the distance across the circle through its center), then divide the diameter by 2 to get the radius. Then use the formula:

π×r2

How to measure multi-story homes

Each level should be measured separately and totaled. The overall square footage includes all finished areas across all floors but excludes unfinished attics and basements.

How to measure open floor plans

For open-concept spaces without distinct room divisions:

1. Measure the full length and width of the open area.
2. Subtract areas not considered livable space (e.g., stairwells, unheated sunrooms).

Why accurate square footage matters

Having precise square footage measurements is crucial for:

• Real estate listings: Buyers use price per square foot for home comparisons.
• Home appraisals: Square footage influences property valuation.
• Renovations: Accurate dimensions aid in material selection and budgeting.
• Property taxes: Local governments base taxes on your home’s square footage.

Square footage is a critical factor in a home’s value, so both buyers and sellers should ensure the measurement is precise. Even minor discrepancies can impact pricing, appraisals, and negotiations. Consider the following for each party involved:

For sellers: avoid overestimating or underestimating your home’s size

• Verify, don’t assume: As-built square footage may differ from original plans due to construction changes. Always measure independently or hire a professional appraiser.
• Avoid pricing errors: Listing with incorrect square footage can lead to mispricing, potentially deterring buyers if discrepancies arise during appraisal or inspection.
• Legal and ethical obligations: Misrepresenting square footage, even unintentionally, can result in legal issues or demands for price reduction from buyers. Some states mandate accurate home measurements under disclosure laws.

For buyers: don’t rely solely on listed numbers

• Confirm the measurements: Real estate listings may use outdated or inaccurate square footage from tax records. Request recent appraisals or conduct your measurements.
• Understand what’s