What's the square footage?
Add rooms, lots or yards of any shape, get square feet, yards, acres and cost instantly.
How do I calculate square footage?
Multiply the length by the width, both in feet. A 12 by 15 ft room is 12 × 15 = 180 square feet. For an L-shaped room or a yard with odd corners, split it into rectangles, measure each one and add them up — use + Add another area for each piece.
How do I find the square footage of a circle or a triangle?
A circle is π × radius²: an 8 ft round patio has a radius of 4 ft, so 3.1416 × 4 × 4 = 50.3 square feet. A triangle is base × height ÷ 2: a triangle 10 ft along the base and 6 ft tall is 30 square feet. Pick Circle or Triangle on the area and enter the sizes.
How many square feet are in a square yard and in an acre?
A square yard is 3 ft × 3 ft = 9 square feet, so divide square feet by 9 to get square yards — carpet and sod are often priced that way. An acre is 43,560 square feet; a quarter-acre lot is 10,890.
How do I convert square feet to square meters?
Multiply by 0.0929: 200 square feet is 18.6 square meters. To go the other way, multiply square meters by 10.764. Switch the calculator to Metric and your sizes are converted for you.
How is the square footage of a house measured?
Real-estate listings in the US usually follow the ANSI Z765 standard: finished, heated living space measured to the outside of the exterior walls, with garages and unfinished basements left out. For flooring or paint, measure each room from wall to wall instead — that is the area you will actually cover.
How do I measure a room that is not a rectangle?
Split it into rectangles (and triangles or circles where needed), find the area of each and add. An L-shaped room made of a 20 by 12 ft main part and an 8 by 10 ft wing is 240 + 80 = 320 square feet. Do not multiply the overall length by the overall width of the L: that counts the empty corner as floor.
How do I enter feet and inches, such as 12 ft 6 in?
Convert the inches to a fraction of a foot by dividing by 12: 6 inches is 0.5 ft, so 12 ft 6 in is 12.5 ft, and 9 ft 3 in is 9.25 ft. A room 12 ft 6 in by 9 ft 3 in is 12.5 × 9.25 = 115.63 square feet.
What the calculator does
Each area is length times width for a rectangle (or the circle and triangle formulas for those shapes), and the calculator adds all the pieces you enter. The extra percentage is applied to the total, and the result is shown in square feet together with square yards, square meters and acres. The conversion factors are exact: a square yard is 9 square feet, an acre is 43,560 square feet, and a square foot is 0.09290304 square meters, because a foot is defined as exactly 0.3048 meters. The price table turns the total into a cost using whichever unit the seller quotes.
Worked example: flooring for an L-shaped room
The room is 240 + 80 = 320 square feet. Flooring is cut and fitted, so add 10% for waste: 320 × 1.1 = 352.0 square feet to buy. That is 29.7 square meters of floor, or 35.6 square yards. If carpet is priced at $4.50 per square foot, the same carpet costs $40.50 per square yard, because there are 9 square feet in each. Always check which unit a price is quoted in; a figure of $40.50 looks very different next to a per-foot price of $4.50 although it is the same carpet.
Square feet in other units
Some common conversions follow from the exact factors above. 100 square feet is 9.29 square meters, and 100 square meters is 1,076.4 square feet. A quarter acre is 10,890 square feet. A square 66 ft by 66 ft is 4,356 square feet, one tenth of an acre. For small areas, remember that one square foot holds 144 square inches, which matters when you measure tiles and trim in inches.
Common mistakes
The first is mixing units, such as multiplying a length in feet by a width in inches; convert before multiplying. The second is confusing square feet with linear feet: a 12 foot board is 12 linear feet and covers area only once you multiply by its width. Third, measuring to the outside of the walls gives a larger number than the floor you will actually cover, which is the standard for listing a home but not for ordering flooring. And skipping fixed items matters: enter cabinets, a fireplace hearth or a kitchen island as a separate area only if the floor will not run under them.
Sources: exact unit factors from NIST Special Publication 811, Appendix B.8 (the international foot is 0.3048 m; the acre is 43,560 square feet by the US survey definition, which differs from the international acre by a few parts per million); house measuring practice from ANSI Z765 as noted above. Related: area calculator, flooring calculator and square yards calculator.