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The Home Depot

Square Footage Calculator

Pro Referral > Home Guides > General Contracting > Square Footage Calculator

Utilize our easy-to-use square footage calculator for projects big and small. Whether you’re looking to calculate the size of a room or your entire home, we can help you arrive at an accurate number to ensure you have the information you need to buy, sell, renovate, or remodel your home.

Width (ft):

Length (ft):


Square footage =

How To Calculate Square Footage of a Room

Prospective home buyers, professionals, renters, and real estate agents will find that measuring the square footage of a square or rectangular room is as easy as multiplying the length and width of your room’s walls. And since some projects can be more in-depth than others, we’ve broken down the exact calculations below for some of the most common home projects.

Calculate Square Footage for Painting

1. Calculate the square footage of a room’s walls by adding together the length of all the walls and then multiply that number by the height of the room, from floor to ceiling.

    Example: A room with 8 foot walls is 14 feet wide by 16 feet long.

    (14 feet + 14 feet + 16 feet + 16 feet) x 8 feet = 480 square feet

2. To determine how much paint you will need to buy, subtract the square footage of all windows and doors. The average window is 15 square feet and the average door is 20 square feet.

    Example: The room has two windows and two doors.

    480 sq. ft. - (2 x 15 sq. ft.) = 450 square feet

    450 sq. ft. - (2 x 20 sq. ft.) = 410 square feet

    Total = 410 square feet

3. If you decide to paint the trim in your room as well, be sure to measure the entire length of all the trim features, including door and window trim, crown molding, and baseboard. Most trim elements range from about 3 to 6 inches, so multiply the total length by the appropriate fraction of 1 foot in order to determine the total square footage. To include the doors, simply estimate 20 square feet or multiply their height by their width and add the figure to your total (double the amount if painting both sides).

    Example: The room has 40 linear feet of 3-inch-wide window and door trim, 54 linear feet of 4- inch-wide baseboard, and two doors to paint on one side.

    (54 ft. x .33 ft.) + (40 feet x .25 ft.) = 27.82 (28) square feet

    20 square feet x 2 doors = 40 square feet

    Total = 68 square feet

4. If you are painting the ceiling along with your walls, follow these simple steps and add the ceiling size to your total room square footage. First measure the room's width then the room's length. Multiply the width and the length measurements to determine the total ceiling area.

    (Example: The room is 14 feet wide and 16 feet long.

    (14 feet x 16 feet = 224 square feet

    Total = 224 square feet

5. Remember that you will probably need multiple coats of paint or primer, so buy enough material to allow for the coverage required.

    Example: One coat of primer and two coats of paint to cover 410 square feet of wall space.

    410 sq. ft. x 1 = 410 sq. ft. of primer

    410 sq. ft. x 2 = 820 sq. ft. of paint

Calculate Square Footage for Carpet Installation

1. Once you've determined the simple square footage of the room you're carpeting, you will need to add an extra 10 percent to your carpet order for cutting, waste, and staggering the carpet joints. Be sure to measure from the widest part of the room if it is shaped irregularly.

    Example: A 10 x 10 room has 100 square feet of floor to carpet.

    10 feet x 10 feet = 100 square feet

2. If your room features a closet or alcove, remember to include the extra space in the total square footage.

    Example: A 3 by 3 foot closet needs to be included in measuring.

    3 ft. x 3 ft. = 9 square feet

    100 sq. ft. + 9 sq. ft. = 109 square feet

3. Add 10 percent to allow for cuts and waste and round up to the next whole number.

    109 sq. ft. x 10% = 10.9 sq. ft.

    109 sq. ft. + 10.9 sq. ft. = 119.9 sq. ft.

    Total = 120 square feet

4. Carpet is often sold by the square yard, so you may need to convert your totals to simplify shopping. To convert square feet to square yards, simply divide the total by 9.

    120 square feet ÷ 9 = 13.33 square yards

    Total = 14 square yards

5. Remember that most carpet installations require padding, so be sure to plan for the same square footage or yardage of padding as carpet.

6. Installing carpet also usually calls for 4-foot-long tack strips that are secured around the perimeter of the room, except in doorways. To measure for the strips, simply add together the length of each wall and subtract the width of doorways.

    Example: A 10 foot by 10 foot room with two doors requires tack strips.

    (10 ft. + 10 ft. +10 ft. + 10 ft.) – (3 ft. + 3 ft.) = 34 feet

    34 ft. ÷ 4 ft. = 8.5 pieces

    Total = 9 four-foot lengths

Calculate Square Footage for Wallpaper Installation

1. Measure walls for wallpaper in the same way you would for paint.

    Example: A room with 8 foot walls is 14 feet wide by 16 feet long.

    (14 feet + 14 feet + 16 feet + 16 feet) x 8 feet = 480 square feet

2. Since there can be variations between different dye lots of wallpaper, stay on the safe side and don’t subtract the area of doors and windows from your initial calculations. Go a step further by adding 10 percent for waste and trimming.

    (Example: Add 10 percent for coverage of 480 square feet.

    (480 square feet x 10% = 48

    (480 sq. ft. + 48 sq. ft. = 528 sq. ft.

    Total = 528 square feet

3. Wallpaper is sold in rolls with standardized coverage. Divide the total square footage by the coverage of the wallpaper to find out how many rolls to buy.

    Example: A double roll of wallpaper covers 56 square feet.

    528 square feet ÷ 56 = 9.4 rolls

    Total = 10 rolls

4. If your wallpaper requires pattern matching, check the frequency of the pattern repeat on the label and calculate the number of rolls needed according to the usable square footage of the roll. You may need several extra rolls in order to perfect the pattern alignment.

How to Calculate the Square Footage of a Home

The method used to calculate the square footage of an entire home is the same as that used for a room, just based on the perimeter of the entire building and multiplied by the number of living levels. It can be helpful to know the overall square footage of your home for planning various whole-house renovations and maintenance or for cost comparisons for buying, selling, or renting a property.

Buying and Selling

1. Buyers, sellers, and agents use the square footage of a home to provide a baseline of price comparison between properties or to give an idea of the useable space inside a home. In real estate listings, typically only finished or conditioned living spaces are included in the total square footage figure, so keep in mind that unfinished spaces, such as basements, garages, or unheated rooms, may not be included in the total.

    Example: Comparing a 2,500 square foot house listed at $300,000 with a 2,100 square foot house listed at $275,000.

    $300,000 ÷ 2,500 = $120/sq. ft.

    $275,000 ÷ 2,200 =$125/sq. ft.

2. To calculate the square footage of a square or rectangular house, simply multiply the length by the width of the building. If the home is an irregular shape, it may be necessary to measure the home in sections and add the totals together, or use different formulas to calculate the area of spaces in a circular, triangular, or other shape. Be sure to multiply or add the area of additional stories and deduct the area of unfinished spaces that fall within the footprint measured.

    Example: A 36 foot long and 28 foot wide two story home with a 16 by 20 foot single story home office addition.

    (36 feet x 28 feet) x 2 = 2016 sq. ft. main house

    16 feet x 20 feet = 320 sq. ft. addition

    Total = 2336 square feet

Renovating and Maintenance

1. The total square footage of a home is often used by contractors to provide pricing for finish materials like flooring or services such as pest control, but also may be used for rough estimations on wiring, plumbing, and HVAC systems or for general renovations. Area is also used for evaluating energy efficiency or heating and cooling demand, but in many cases, the volume, or cubic footage, of the house must be known to make accurate calculations. To determine the volume of a rectangular house, multiply the length by the width by the height of each level and add the totals.

2. The square footage of exterior walls is needed to calculate paint and siding materials, and is used for pricing services like pressure washing. Like the interior walls, the surface area is determined by multiplying the length by the height of each wall and subtracting the area of doors and windows. This is pretty straightforward on rectangular walls, but can get a little tricky when measuring a gable end wall. If you know the pitch of the roof or if you can measure the height of the triangular area from the eave to the peak, multiply the width of the base by the height of the triangle and divide by two. Add the result to the area of the remaining rectangular wall below to find the square footage of the entire wall.

    Example: A gable end wall 28 feet wide with two full stories, each 10 feet high, and an additional 8 feet to the peak.

    (28 feet x 20 feet) + ((28 feet x 8 feet) ÷ 2) = 672 square feet

3. If you cannot safely measure the height of a gable wall, try counting the courses of siding to estimate the total height. Just measure the width of one course of siding, multiply by the number of courses you count, and convert your measurement from inches to feet.

    Example: Eighty four courses of lap siding with a four-inch reveal.

    84 x 4 inches = 336 inches

    336 in. ÷ 12 = 28 feet

4. Siding materials are often sold by the “square” or 100 square feet of coverage. To calculate the number of squares needed for a project, add 10 percent for cuts and waste and divide the total square feet by 100.

    Example: Siding for a wall with area of 672 square feet.

    672 sq. ft. x 10% = 6.72 sq. ft.

    (672 sq. ft. + 6.72 sq. ft.) = 6.79 squares

    Total = 7 square of siding

Calculating the square footage of a wall, a room, or an entire home comes down to the basic geometry of area, but figuring out irregular or complex layouts can be a little challenging. To solve these puzzles, figure out what surfaces are relevant for your project and break them down into measurable shapes. Just calculate the area for each shape and add the figures together to come up with the grand total you will need for any project.

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