BuildMath

Square footage calculator

A 12 × 15 ft room is 180 square feet, or 20 square yards. Add another rectangle for an L-shape, or subtract an island.

Shape
Length
Width
Waste
Common rule of thumb, adjust to your layout.

You need 180.00 square feet (20.00 sq yd, 16.72 m²).

That is 20.00 square yards (16.72 square meters).

Report a problem with this result
12 ft15 ft
How we calculated this

12 × 15 ft (180 square feet) = 180 square feet.

180 square feet = 20 square yards (180 ÷ 9) = 16.72 square meters.

NIST lists 1 acre as 43,560 square feet. This page shows acres when the total is over 1,000 square feet.

No extra was added for waste. 5%, 10%, and 15% are a common rule of thumb for flooring; leave this off for a house or room total.

Estimate cost (optional)

Sources

One acre is 43,560 square feet (NIST U.S. survey-foot conversion tables (federal agency) (opens in a new tab); NIST Handbook 44 Appendix C). Square yards are square feet ÷ 9.

Finished house area follows Fannie Mae Selling Guide B4-1.3-05 (GSE) (opens in a new tab), which requires ANSI Z765-2021 for single-family dwellings, and HUD Handbook 4000.1 (federal agency) (opens in a new tab) Gross Living Area: finished, habitable, above-grade space. Garage and basement are reported separately. Local practice and appraisers vary. Flooring waste chips of 5%, 10%, and 15% are a common rule of thumb, not a cited table.

Square footage calculator

A 12 × 15 ft room is 180 square feet, or 20 square yards (16.72 square meters). Split an L-shape into rectangles and add them. Mark an area Subtract to drop an island, hearth, or closet you are not covering.

  1. Enter length and width in feet. Open More options and choose Feet + inches to type a tape reading such as 12 ft 6 in. Metric units are on the same fields.
  2. Use Add another area for a second room or the short leg of an L. Each extra area can be a rectangle, circle, or triangle, and can be marked Subtract.
  3. Leave waste on None for a room or house total. For flooring, 5%, 10%, or 15% is a common rule of thumb.
  4. Open Estimate cost and type a price per square foot if you have a quote. There is no default price.

Length × width gives square feet. Add extra areas for an L-shape. Divide square feet by 9 for square yards. One acre is 43,560 square feet (NIST).

How to calculate square footage

Multiply length by width in feet. A 12 × 15 ft room is 180 square feet. For an L-shape, split the floor into rectangles and add them: 12 × 15 plus 6 × 8 is 228 square feet. Square feet = length × width. Convert to square yards by dividing by 9.

Worked example: L-shaped room, 12 × 15 plus 6 × 8

Worked example

Split the L into a 12 by 15 ft rectangle and a 6 by 8 ft rectangle.

12 × 15 = 180 square feet. 6 × 8 = 48 square feet. 180 + 48 = 228 square feet. 228 ÷ 9 = 25.33 square yards.

Those two rectangles are the Add another area pattern on this page. Subtract a 3 × 4 ft island from the 12 × 15 room and the net is 168 square feet.

Common room sizes

RoomSquare feetSquare yards
10 × 10 ft10011.11
10 × 12 ft12013.33
12 × 12 ft14416.00
12 × 15 ft18020.00
15 × 20 ft30033.33
20 × 20 ft40044.44

A 10 ft circle is π × 5² = 78.54 square feet. This page shows acres only when the total is over 1,000 square feet. 43,560 square feet is 1 acre.

We do not show a national floor-covering price. Open Estimate cost and type a price per square foot from your quote. This page estimates material area, not labor, unless you type a combined figure.

Questions

How do you figure out the square footage of a room?
Multiply the length by the width in feet. A 12 × 15 ft room is 180 square feet. If the room is not a rectangle, split it into rectangles, a triangle (base × height ÷ 2), or a circle (π × radius²) and add the pieces.
How do you calculate the square footage of a house?
Add the finished rooms on each above-grade floor. Fannie Mae (Selling Guide B4-1.3-05) requires ANSI Z765-2021 for single-family dwellings: report finished above-grade area separately from below-grade area. HUD Handbook 4000.1 Gross Living Area is finished, habitable, above-grade space. Rules still vary by local practice and appraiser, so keep garage and basement as separate totals.
How do I calculate square footage with inches?
Convert inches to feet by dividing by 12, then multiply. 12 ft 6 in is 12.5 feet; 12.5 × 10 ft is 125 square feet. This page accepts 12 ft 6 in or 12' 6" when you choose Feet + inches under More options.
Does square footage include the garage?
Not in finished above-grade living area under ANSI Z765-2021 as applied by Fannie Mae. A garage is reported separately. Some listings still add it. Local practice and the appraiser can differ, so say whether your number includes the garage.
Is the basement included in square footage?
Not in above-grade living area under the Fannie Mae and HUD sources cited on this page. Fannie Mae (Selling Guide B4-1.3-05) requires ANSI Z765-2021 for single-family dwellings and reports finished above-grade area separately from below-grade area. HUD Handbook 4000.1 Gross Living Area is finished, habitable, above-grade space and reports a finished basement on another line. Exact ANSI wording is not quoted here. Rules vary by appraiser and local listing practice.
How many square feet are in an acre?
43,560 square feet. NIST Handbook 44 Appendix C and the NIST U.S. survey-foot conversion tables list 1 acre as 43,560 ft². This calculator shows acres when the total is over 1,000 square feet.
How do I measure square footage for flooring?
Tape each room wall to wall, add the rectangles (and subtract islands you will not cover), then add waste. 5%, 10%, and 15% extra are a common rule of thumb for cuts and pattern; leave waste off if you only want the floor area. Open Estimate cost to type a price per square foot.
How do I calculate the square footage of a wall?
Use the same rectangle math: wall length times wall height in feet. A 12 ft wall that is 8 ft high is 96 square feet. Subtract a window or door as a second area marked Subtract. This page is built for floors and rooms; a wall is one more rectangle.

Written by The BuildMath team. Formulas tested against worked examples. Updated October 24, 2026.