How to Measure your Floor Area

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.


Net Floor Area (NFA)

Net floor area is used to calculate occupant load based on building codes. It is measured to the inside face of a room’s walls. Net floor area does not include accessory areas as described below.

Net Floor Area is defined by the 2018 International Building Code as:

The actual occupied area not including unoccupied accessory areas such as corridors, stairways, ramps, toilet rooms, mechanical rooms and closets.

How to find the square footage of a circle

  1. Measure the diameter of your circle in feet.
  2. Divide your diameter by 2 and then square it (multiply it by itself).
  3. Multiply your total by π (3.14159265)

The formula for calculating the area of a circle is: π r2 (with r being the radius of the circle, which is half the diameter). π is the symbol for pi (3.14159265).


BOMA Gross Area 4 – Construction Method

BOMA/ANSI Z65.3, Gross Area 4 replaces the previous Construction Gross Area (CGA) and is used for estimating construction costs or maintenance costs. It was introduced in ANSI/BOMA Z65.3-2018. Gross Area 4 represents the largest square footage calculation since it includes all areas.

The BOMA Gross Areas of a Building: Standard Methods of Measurement, 2018 identifies BOMA Gross Area 4 as the sum of all areas within the boundary lines of Space Classifications A, B, C, D, E, and F. This includes the following:

  • Space Classification A: Floor Area, Parking Area, and Connectors
  • Space Classification B: Balconies, Exclusive Use Covered Galleries, and Finished Rooftop Terraces
  • Space Classification C: Unenclosed Occupant Circulation and Roofless Structured Parking
  • Space Classification D: Public Use Covered Galleries and Sheltered Area (Industrial)
  • Space Classification E: Building Voids
  • Space Classification F: Other Rooftop Areas, Unenclosed Connectors, Decks, and Plazas

The following images depict Gross Area 4 for a simple building in cyan:

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.

What to know about FAR violation?

An FAR violation by a developer usually comes to light, only when the relevant development authority issues a completion certificate. Therefore, home buyers should ask to see the completion certificate, before buying a property in the project. Buying a property in a project that has violated the FAR regulations of the city/locality, could have serious repercussions on your credit worthiness, if you were to apply for a loan.

How to Calculate Square Footage

Square footage is area expressed in square feet. Likewise, square yardage is area expressed in square yards.  Square meters is also a common measure of area.

Assume you have a rectangular area such as a room and, for example, you want to calculate the square footage area for flooring or carpet.

The way to calculate a rectangular area is by measuring the length and width of your area then multiplying those two numbers together to get the area in feet squared (ft2). If you have on oddly shaped area, such as an L-shape, split it into square or rectanglualar sections and treat them as two separate areas. Calculate the area of each section then add them together for your total. If your measurements are in different units, say feet and inches, you can first convert those values to feet, then multiply them together to get the square footage of the area.

Convert all of your measurements to feet

  • If you measured in feet skip to “Calculate the Area as Square Footage”
  • If you measured in feet & inches, divide inches by 12 and add that to your feet measure to get total feet
  • If you measured in another unit of measure, do the following to convert to feet – inches: divide by 12 and that is your measurement in feet – yards: multiply by 3 and that is your measurement in feet – centimeters: multiply by 0.03281 to convert to feet – meters: multiply by 3.281 to convert to feet

Calculate the Area as Square Footage

  • If you are measuring a square or rectangle area, multiply length times width; Length x Width = Area.
  • For other area shapes, see formulas below to calculate Area (ft2) = Square Footage.

How many square feet is a 12×12 room?

The square footage of a room measuring 12 feet wide by 12 feet long is 144 square feet. To calculate this you simply multiply the width by the height. 12ft × 12ft = 144 sq ft.


Is FAR and FSI the same? Yes, these are used synonymously. FAR is the Floor Area Ratio and FSI stands for Floor Space Index. This ratio is determined by dividing the built-up area of a building with the total size of the plot.

What is 2.5 FSI? If the FSI is 2.5, this means that a builder with a plot of 1,000 sq metres, can construct 2.5×1,000 sq metres, that is 2,500 sq metres, according to FSI calculation formula.

What is GFA? GFA refers to Gross Floor Area and is used to calculate FAR. tenant area, meeting rooms, mechanical equipment area, stairwell, lobbies, restrooms, etc., are included in the GFA.

What is a good floor area ratio? Most developers look for a high FAR. However, a good floor area ratio will also depend on the city and different localities within the city. In metropolitan cities such as Delhi, the FAR ranges from 1.25 to 3.

Does floor area ratio include garage? The floor area ratio does not include unoccupied spaces like parking, garages, etc.

What is floor area ratio formula? The Floor Area Ratio (FAR) is calculated as per the formula: Floor Area Ratio (FAR) = Total area of the building / plot size.

(With inputs from Sneha Sharon Mammen and Harini Balasubramanian)

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