Square footage calculator
Enter the length and width of a room to get its area in square feet, square yards and square meters. Add more rectangles, a triangle or a circle for a larger space, and take away what is not part of it.
This answer is for the example values in the boxes above. rectangle 12 by 10 feet, rectangle 6 by 4 feet. Change the boxes to see your own answer.
The areas of the shapes are added and the part taken away is subtracted. A room in the shape of an L is two rectangles.
How it works
Pick the unit that you measured in: feet, inches, yards, meters or centimeters. Fill in a length and a width for each rectangle, a base and a height for a triangle, and a diameter for a circle. The calculator finds each area in the square of your unit, adds them, takes away the part you entered, and converts the total.
The conversions are exact. A foot is 0.3048 meter, an inch is 0.0254 meter and a yard is 0.9144 meter, so a square foot is exactly 0.09290304 square meter. A square yard is 9 square feet.
A worked example
A room 12 feet by 10 feet is 120 square feet. An alcove 6 feet by 4 feet adds 24, for 144 square feet in all, which is 16 square yards or 13.38 square meters.
In meters, a room 4 by 3 is 12 square meters, or 129.17 square feet. A triangle with a base of 10 and a height of 6 feet is 30 square feet, and a circle 10 feet across is 78.54. Added to the first room, they make 228.54 square feet.
Spaces that are not one rectangle
An L-shaped room is two rectangles. A triangular nook is a triangle, and a round patio or a circular alcove is a circle, each added to the main rectangle. A wall is a rectangle as well: its length times its height, with a window or a door in the take away box.
What it leaves out
The calculator gives an area, not an amount to buy. A box of flooring or a can of paint has its own coverage, and the tile and paint calculators work from the area to the amount. For a house that is for sale, a listing or an appraiser may follow its own rules about which rooms count, while this calculator adds the shapes that you give it.
Sources
- NIST Special Publication 811, Appendix B.8: factors for units listed alphabetically, read on 2026-11-01.
Questions
How do I calculate the square footage of a room?
Multiply the length by the width, both in feet. A room 12 feet long and 10 feet wide is 12 times 10, which is 120 square feet.
How do I find the area of a room that is not a rectangle?
Split it into rectangles, find the area of each and add them. A 12 by 10 room with a 6 by 4 alcove is 120 plus 24, or 144 square feet.
How many square feet are in a square yard?
Nine, because a yard is 3 feet and 3 times 3 is 9. So 144 square feet is 16 square yards.
How do I convert square feet to square meters?
Multiply by 0.09290304, which is exact. 144 square feet is 13.37803776 square meters, shown as 13.38.
How do I find the area of a circle or a triangle?
For a circle, multiply pi by the radius squared; the calculator asks for the diameter, which is twice the radius. For a triangle, multiply the base by the height and halve it. A circle 10 feet across is 78.54 square feet, and a triangle with a base of 10 and a height of 6 is 30.
How do I leave out a doorway or a closet?
Fill in its length and width in the take away box. The calculator subtracts it from the total, so 144 square feet less a 3 by 2 doorway is 138 square feet.
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