Square Footage Calculator
Area of a room, a lot or an odd shape from rectangles, triangles and circles added together, in square feet, yards, metres and acres with exact factors.
Quick answer: square footage from shapes
| Shape | Formula | Area |
|---|---|---|
| Rectangle 15 × 12 ft | length × width | 180 ft² |
| Triangle, base 10, height 8 ft | base × height ÷ 2 | 40 ft² |
| Circle, 10 ft across | π × (diameter ÷ 2)² | 78.54 ft² |
| Total | added | 298.54 ft² |
These are the calculator's defaults: 298.54 ft², which is 33.17 yd² or 27.74 m². Split an odd plan into rectangles, triangles and circles, add them, and enter −1 to subtract a part that is not floor.
Up to four shapes, added together. Leave a shape’s dimensions blank to skip it; use the negative quantity to subtract a cut-out.
| 1 | — |
|---|---|
| 2 | — |
| 3 | — |
| 4 | — |
| Square feet | — |
| Square yards | — |
| Square metres | — |
| Acres | — |
Any floor plan is rectangles, triangles and circles. An L-shaped room is two rectangles; a bay window is a rectangle and two triangles; a round patio is a circle. Measure each piece, add them, and subtract the pieces that are not floor, such as a stair opening or an island, with a negative quantity. Four shapes cover most rooms; a plan that needs more is worth drawing rather than adding.
The factors are exact, not rounded. A square foot is 0.09290304 m² by definition, a square yard is 9 ft², an acre is 43,560 ft². Rounded factors like 0.093 are fine for a room and wrong by a bathroom on an acre; the page uses the definitions and rounds only what it prints.
Measured to what? Flooring wants the finished floor, wall to wall. A lease wants the rentable area, which includes things you cannot stand on. A lot wants the survey. The number is only as good as the question it answers, and this page answers the one you measured.
If the number is going into a mortgage appraisal, there is a rulebook, and local custom does not override it. Fannie Mae has required ANSI Z765-2021 for appraisals with effective dates on or after April 1, 2022, and its FAQ answers the question of adjusting a house's area to local practice with one word: no. An appraiser who cannot comply has to enter the exception code GXX001 and say why; Fannie Mae's own example is a berm house with all of its area below grade.
Five rules decide which of your rectangles count. Measure the outside, to the nearest inch or tenth of a foot, and report the total to the nearest whole square foot. A level partly or completely below grade is basement, not living area. The void over a two-storey space is not floor. A stair counts once, on the floor it descends from. Finished area needs a 7 ft ceiling, and in a room under a slope at least half of the finished floor must reach 7 ft while nothing under 5 ft counts.
This page adds shapes; it does not decide which shapes are living area. Enter the basement, the garage and a low attic room as separate shapes and you can report them on separate lines, which is what the standard does with area that does not qualify. ANSI Z765 is a United States standard for single-family houses; a flooring or paint order still wants the inside dimensions, wall to wall.
What I check on a job
How I catch a wrong total. Before I trust the total, I check each connected space against one rough rectangle: its overall length times its overall width. For one room, the real figure should come in at or under that box, and if it comes in over, a shape went in twice or a cut-out went in with the wrong sign. A detached patio or deck gets its own box. I tape each wall at both ends, because older rooms are rarely square and a wall that runs longer at one end changes the rectangle you think you have. On the triangle, the height is the distance square to the base, not the length of the sloped side; using the slope inflates a bay every time. A circle's diameter has to pass through the center, so I take the longest measurement across rather than the first one. And I write the measured face next to every figure, because a number taken for one purpose tends to get reused weeks later for a flooring order.
Rectangle = length × width; triangle = ½ base × height; circle = π (d ÷ 2)². Totals use 1 ft² = 0.09290304 m² (exact), 1 yd² = 9 ft², 1 acre = 43,560 ft².
Worked example
A 15 × 12 ft room with a triangular bay 10 ft wide and 8 ft deep, and a round 10 ft patio: total square footage?
- Rectangle 15 × 12 = 180 ft²; triangle ½ × 10 × 8 = 40 ft²; circle π × 5² = 78.54 ft².
- Total 298.54 ft².
- ÷ 9 = 33.17 yd²; × 0.09290304 = 27.74 m²; ÷ 43,560 = 0.00685 acre.
298.5 square feet, or 33.2 square yards. A cut-out — a stair opening, an island — goes in as a shape with quantity −1.
7 values on this page were driven in a browser and compared with independently derived figures on 2026-10-29 (2808 values across 228 calculators site-wide).
Questions
How do you calculate square footage of an L-shaped room?
As two rectangles added together: measure each leg's length and width, multiply, and sum. A cut-out is a rectangle subtracted.
How many square feet in a square yard and an acre?
9 and 43,560. A square metre is 10.7639 ft² (1 ft² = 0.09290304 m² exactly).
Which areas count as living area in an appraisal?
Under ANSI Z765-2021, which Fannie Mae has required since April 1, 2022: measure the outside, count no level that is even partly below grade, leave out open-to-below space, count a stair once on the floor it descends from, and count finished area only where the ceiling is at least 7 ft (at least half of a sloped room, nothing under 5 ft).
Does rounding 0.0929 to 0.093 matter?
Not on a room, but on an acre the rounded factor is off by about 4.2 m², a bathroom. A square foot is 0.09290304 m² exactly; the page uses the definition and rounds only what it prints.