How to Calculate Square Footage
How to calculate square footage for rectangles, L-shaped rooms, triangles and circles, convert sq ft to m², add a flooring waste allowance and price per sq ft.
By Udit Agarwal · Updated October 17, 2026
To calculate square footage, measure the length and width of a space in feet and multiply them: a room 12 feet long and 10 feet wide is 12 × 10 = 120 square feet. Rooms that are not rectangles are split into rectangles, triangles and circles, each worked out separately and then added together. Multiply the area by a price per square foot, add a waste allowance, and you have the basis of a flooring, tile or turf estimate.
Area = length × width, with both measurements in feet. The answer is in square feet (sq ft or ft²) because you multiplied feet by feet. A 15 ft by 11 ft bedroom is 165 sq ft, and a 6 ft by 4 ft rug is 24 sq ft.
Tape measures give feet and inches, so turn the inches into a decimal of a foot first by dividing by 12. A room 12 ft 6 in by 10 ft 3 in is 12.5 ft × 10.25 ft = 128.125, or about 128.13 sq ft. Writing it as 12.6 × 10.3 is a common slip: 6 inches is half a foot, not six-tenths, and the wrong version gives 129.78 sq ft.
| Inches | Feet | Inches | Feet |
|---|---|---|---|
| 1 | 0.083 | 6 | 0.5 |
| 2 | 0.167 | 8 | 0.667 |
| 3 | 0.25 | 9 | 0.75 |
| 4 | 0.333 | 10 | 0.833 |
You can also measure everything in inches and divide the result by 144, the number of square inches in a square foot: 150 in × 123 in = 18,450 sq in, and 18,450 ÷ 144 = 128.125 sq ft.
Split an irregular room into rectangles that do not overlap, find the area of each and add them up. Sketch the floor plan first and write each measurement on it. Take an L-shaped room whose main part is 20 ft by 12 ft, with a 10 ft by 8 ft wing off one side:
You can also work from the outside in. Draw the smallest rectangle that encloses the whole room and subtract the missing corner: here the enclosing rectangle is 20 ft by 20 ft, or 400 sq ft, and the missing corner is 10 ft by 8 ft, so 400 − 80 = 320 sq ft again. Getting the same number both ways is a good check on your measurements.
Closets, alcoves and bay windows are extra pieces to add if the new floor runs into them. Areas the floor will not cover, such as the space under fitted kitchen cabinets, can be left out.
| Shape | Formula | Example | Area |
|---|---|---|---|
| Rectangle | length × width | 12 ft × 10 ft | 120 sq ft |
| Triangle | ½ × base × height | base 8 ft, height 5 ft | 20 sq ft |
| Circle | π × radius² | radius 6 ft | 113.10 sq ft |
| Half circle | π × radius² ÷ 2 | radius 4 ft | 25.13 sq ft |
| Trapezoid | (side a + side b) ÷ 2 × height | parallel sides 10 ft and 6 ft, 5 ft apart | 40 sq ft |
A triangle's height is measured at a right angle to the base, not along the sloping side; in a right-angled corner, the two sides that meet at the square corner are the base and the height. A circle's radius is half its diameter, so a round patio 12 ft across has a radius of 6 ft and an area of π × 36 ≈ 113.10 sq ft. Putting the diameter where the formula wants the radius makes the answer four times too big. For trapezoids, parallelograms and ellipses, the Area Calculator has the formulas built in.
Since the international agreement of 1959, one foot has been exactly 0.3048 metres. One square foot is therefore 0.3048 × 0.3048 = 0.09290304 m², and one square metre is about 10.7639 sq ft. To convert, multiply square feet by 0.092903 to get square metres, or square metres by 10.7639 to get square feet.
| Area | Equals |
|---|---|
| 100 sq ft | 9.29 m² |
| 120 sq ft | 11.15 m² |
| 1,000 sq ft | 92.90 m² |
| 2,000 sq ft | 185.81 m² |
| 10 m² | 107.64 sq ft |
| 20 m² | 215.28 sq ft |
| 50 m² | 538.20 sq ft |
| 100 m² | 1,076.39 sq ft |
The trap is using the length factor on an area. 120 sq ft × 0.3048 gives 36.58, which is wrong: area units are squared, so the conversion factor is squared too, and the right answer is 11.15 m². Carpet in the US is sometimes priced by the square yard, which is 3 ft × 3 ft = 9 sq ft, so a 120 sq ft room is 13.33 sq yd.
Wall area for painting is a different calculation: the distance around the room times the ceiling height, minus doors and windows. The Paint Calculator works it out from the room's dimensions.
Order more material than the floor area. Cuts at the walls, around door frames and at the ends of rows leave offcuts that cannot all be reused, and a few spare pieces are useful for later repairs. About 10% extra is the usual starting point for a straight layout in a simple room. Diagonal and herringbone layouts, and rooms with many corners, waste more, and 15% or more is common. When the flooring manufacturer recommends a figure, use theirs.
Material to buy = area × (1 + waste ÷ 100). For the 320 sq ft L-shaped room with 10% waste, that is 320 × 1.10 = 352 sq ft. Flooring is sold in whole boxes, so divide by the coverage printed on the box and round up: at 22.5 sq ft per box, 352 ÷ 22.5 = 15.64, so buy 16 boxes. The percentage guide explains why adding 10% means multiplying by 1.10, and the Tile Calculator does the whole job for tile, with a waste allowance that starts at 10% and an optional tiles-per-box count.
Total cost = area × price per square foot. At $3.49 per sq ft, the 352 sq ft of flooring above costs 352 × 3.49 = $1,228.48. A price per square metre converts the same way as an area: multiply a price per square foot by 10.7639, so $3.49 per sq ft is about $37.57 per m².
The division also works backwards. A 1,800 sq ft home listed at $360,000 costs $360,000 ÷ 1,800 = $200 per square foot, which is how listings are compared. Treat any figure from these formulas as an estimate rather than financial advice, because real quotes depend on the product, the subfloor and local labor rates.
The Square Footage Calculator works out one shape at a time. Choose Rectangle (length and width), Circle (radius) or Triangle (base and height), pick Feet or Meters, and type the dimensions. The result shows the area in both square feet and square meters, rounded to two decimal places, and the copy button copies a short text summary. It opens with a 12 × 10 ft rectangle, which gives 120.00 sq ft and 11.15 sq m.
Two optional fields extend it. Quantity multiplies the area for several identical rooms or sections and accepts any number above 0. Price per sq ft, or per sq m when Meters is selected, turns the total area into a total cost. The cost is labelled in dollars, but the arithmetic works for any currency. Two 12 × 10 ft rooms at $3 per sq ft come to 240 sq ft and $720.00.
What it does not do, and how to work around it:
The calculation runs in your browser, and the page reminds you that the result is a planning estimate, so re-measure before you order materials.
How do I calculate the square footage of a room? Measure the length and width in feet and multiply them, so a 12 ft by 10 ft room is 120 sq ft. Convert inches to decimal feet first (6 inches is 0.5 ft), and split an irregular room into rectangles and add them up.
How many square feet is a 12x12 room? 12 × 12 = 144 square feet, which is about 13.38 square metres.
How do I convert square meters to square feet? Multiply by 10.7639, so 20 m² is 215.28 sq ft. To go the other way, multiply square feet by 0.092903: 1,000 sq ft is 92.90 m².
How do I find the square footage of an L-shaped room? Split it into two rectangles, find each area and add them. A 20 × 12 ft main area and a 10 × 8 ft wing make 240 + 80 = 320 sq ft. To check, take the enclosing rectangle and subtract the missing corner.
How much extra flooring should I buy? About 10% for a straight layout in a simple room, and 15% or more for diagonal or herringbone patterns or rooms with many corners. Follow the manufacturer's recommendation where there is one, and round up to whole boxes.
How do I calculate the area of a circle in square feet? Multiply π (about 3.1416) by the radius squared, with the radius in feet. A circle 12 ft across has a radius of 6 ft, so its area is 3.1416 × 36 ≈ 113.10 sq ft.
Does ceiling height affect square footage? No. Floor area depends only on length and width. Ceiling height matters for wall area, when painting or hanging drywall, and for sizing heating and cooling, which the BTU Calculator adjusts for.
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