Measure each room's length and width, multiply them, then add all the rooms together

Square footage is the total floor area of your house measured in square feet. To find it, you measure the length and width of each room in feet, multiply those two numbers, and add up all the room totals. For a rectangular room that is 12 feet long and 10 feet wide, you multiply 12 × 10 to get 120 square feet. A house with five rooms of similar size would total around 600 square feet.

You need a measuring tape (a 25-foot tape works well for most rooms), a notebook or phone to record measurements, and a calculator. Measure from the inside of the walls, not the outside, because you want the space you can actually use. If your house has an irregular shape—rooms that jut out or angles that are not 90 degrees—you break those into smaller rectangles, measure each one separately, and add them together.

Key Takeaways

  • Measure the length and width of each room in feet, multiply those numbers, and add all room areas together to get total square footage.
  • Measure from the inside of walls and round to the nearest foot; small measurement errors matter less than consistency across all rooms.
  • Rooms with irregular shapes can be divided into smaller rectangles, each measured and added separately.
  • Basements, attics, and finished spaces count toward square footage only if they have a ceiling height of at least 7 feet and are heated or cooled.
  • Your property deed, tax assessor records, or original home inspection report often list square footage already, saving you the work of measuring.

What to measure and what to skip

Measure every room where you spend time: bedrooms, bathrooms, kitchens, living rooms, hallways, closets, and laundry rooms all count. Measure basements and attics only if they are finished (drywall, flooring, and climate control in place) and have a ceiling height of at least 7 feet. An unfinished basement with exposed joists and concrete does not count, even if you store things there.

Do not measure garages, decks, or porches unless they are fully enclosed and heated or cooled like the rest of the house. Crawl spaces and mechanical rooms (where the furnace or water heater sits) do not count. If you have a second-story room above a garage, measure the room itself—the garage below does not reduce the room's square footage.

How to handle rooms that are not rectangular

Many rooms have corners that stick out, angled walls, or alcoves. Break the room into two or more rectangles. For example, an L-shaped bedroom can be divided into a large rectangle and a smaller rectangle. Measure the length and width of each rectangle separately, multiply each pair, then add the two results together.

If a room has a sloped ceiling (like an upstairs bedroom under a roof peak), measure only the floor area where the ceiling is at least 7 feet high. Measure the length of the room and the width of the section where headroom is adequate, multiply them, and count that area. The part of the room where you cannot stand up does not count.

Recording measurements and doing the math

Write down the room name and its measurements as you go. Use a format like "Master Bedroom: 14 ft × 12 ft = 168 sq ft" so you can check your work later. Measure twice if you are unsure—it takes 30 seconds and catches mistakes. Round each measurement to the nearest foot; measuring to the inch adds false precision when you are working with a tape measure in a lived-in house.

After you have measured every room, add all the square footages together. If your house has a living room (280 sq ft), kitchen (150 sq ft), two bedrooms (120 sq ft and 100 sq ft), one bathroom (40 sq ft), and hallways (60 sq ft), your total is 280 + 150 + 120 + 100 + 40 + 60 = 750 square feet. Write this total down and keep it with your home records.

When to use existing records instead of measuring

Before you spend an hour with a tape measure, check whether someone else has already done the work. Your property deed, the original home inspection report, or your county tax assessor's records often list the house's square footage. Call your county assessor's office (search "[your county] assessor" online) and ask for the square footage on your property record card. Many assessor offices let you look this up online using your address.

Real estate listing sites like Zillow or Redfin show square footage for most houses, though that number comes from public records and may be outdated if you have added a room. If you are buying or selling the house, the real estate agent can provide the official square footage from the listing. For a renovation or remodeling project, the original blueprints or building permit records at your city or county building department will have the measurements.

Why you might need square footage

Homeowners measure square footage for several reasons. If you are selling, the listing price often depends on price per square foot, so an accurate measurement affects your asking price. If you are buying, you want to know what you are paying for. Contractors estimating the cost of new flooring, paint, or HVAC work need square footage to give you an accurate quote. Insurance companies use square footage to set your homeowners insurance premium.

If you are refinancing your mortgage or explore for a home equity loan, the lender may ask for square footage to verify the property value. Some utility companies use square footage to estimate heating and cooling costs. Knowing your house's size also helps you choose the right size air conditioner or furnace if you need to replace one.

Common mistakes to avoid

The most common error is measuring from the outside of the walls instead of the inside. Outside measurements include the thickness of the walls themselves, which inflates the total by several percent. Measure from the inside edge of the wall to the inside edge of the opposite wall. If a wall is shared with a neighbor (in a townhouse or apartment), measure only your side of the wall.

Another mistake is including spaces that should not count. Unfinished basements, garages, and covered porches often get added by accident. Stick to the rule: if it is not heated and cooled like the main living space, or if the ceiling is lower than 7 feet, do not count it. Finally, do not round up or down aggressively. If a room is 12 feet 8 inches, round to 13 feet. If it is 12 feet 3 inches, round to 12 feet. Small rounding errors add up across a whole house.

Frequently Asked Questions

Do I measure the space inside the walls or the thickness of the walls too?

Measure the inside only—from the inside edge of one wall to the inside edge of the opposite wall. This is called "interior square footage" and is the standard for home sales and insurance. The wall thickness itself does not count.

Should I include closets and hallways in my square footage?

Yes. Closets, hallways, and any other enclosed space with a ceiling of at least 7 feet counts toward total square footage. They are part of the usable floor area of your house.

What if my house has a basement that is half finished and half unfinished?

Measure only the finished half—the part with drywall, flooring, and climate control. The unfinished section with exposed concrete and joists does not count, even if you use it for storage.

Can I use my property tax record as my official square footage?

Tax assessor records are a good starting point and often match the real number, but they can be outdated or inaccurate. If you have added a room or finished a basement since the last assessment, your actual square footage is larger. For a real estate transaction, use the number from the official listing or a professional appraisal instead.

Does square footage include the attic if it is finished?

Only if the attic is finished with drywall and flooring, and the ceiling height is at least 7 feet in the areas where you measure. A finished attic bedroom counts fully. A finished attic storage space with a 5-foot ceiling does not count because you cannot use it as living space.