Square Footage Calculator
Pick a shape, enter its dimensions and get the area in square feet, square yards, square meters and acres. You can subtract an area such as a doorway or a pool. Everything runs in your browser.
How to use this square footage calculator
- Choose the shape that matches your space. For an L-shaped room, calculate each rectangle on its own and add the results.
- Pick one unit for every dimension. All sides of the shape use the same unit.
- Enter the dimensions. For a circle, enter the diameter, not the radius. For a triangle, enter the base and the perpendicular height.
- If part of the space should not count, enter its area in square feet in the subtract box.
- Press Calculate. Use Copy result to paste the numbers into a note or quote, or Copy share link to send the same inputs to someone else.
How to calculate square footage
Square footage is the area of a flat surface measured in square feet. One square foot is a square that is 1 foot on each side. The formula depends on the shape, and every length must be converted to feet first.
- Rectangle or square: area = length x width
- Circle: area = pi x radius x radius, where radius = diameter / 2 and pi is about 3.14159
- Triangle: area = base x height / 2
- Square yards = square feet / 9
- Square meters = square feet x 0.092903
- Acres = square feet / 43,560
When you subtract a section, the calculator uses: net area = total area minus the area to subtract.
Worked example
A living room is 18 ft long and 14 ft wide, and has a 4 ft by 3 ft closet cut into one corner that you do not want to count. Total area = 18 x 14 = 252 sq ft. Closet = 4 x 3 = 12 sq ft. Net area = 252 – 12 = 240 sq ft, which is 26.67 square yards or 22.30 square meters.
For a round patio 12 ft across: radius = 6 ft, area = 3.14159 x 6 x 6 = 113.10 sq ft.
Assumptions & limits
- The shapes are flat and have straight sides, or a true circle. Curved or irregular outlines need to be split into simple shapes.
- Dimensions should be measured on the surface you care about. Room area measured wall to wall may differ from the usable or “gross” area quoted in a listing, because listings may follow their own measurement rules.
- The result is area only. Material orders usually need extra for waste, which depends on the product and the layout.
- Results are rounded to two decimals (four for acres).
Frequently asked questions
How do I find the square footage of a room?
Measure the length and width in feet and multiply them. A room 15 ft by 12 ft is 180 sq ft. For irregular rooms, split the floor into rectangles and add their areas.
How many square feet are in a square yard?
There are 9 square feet in a square yard, because 1 yard is 3 feet and 3 x 3 = 9.
How do I convert inches to square feet?
Divide each side by 12 to get feet before multiplying, or enter the sides in inches and let the calculator convert them. A 24 in by 36 in panel is 2 ft x 3 ft = 6 sq ft.
How many square feet are in an acre?
One acre is 43,560 square feet.
Is square footage the same as cubic footage?
No. Square footage is area (two dimensions). Cubic footage is volume (three dimensions) and needs a depth or height as well.
How do I measure a circular area?
Measure across the widest point to get the diameter, halve it for the radius, then use area = pi x radius squared. The calculator does this when you choose Circle.
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Last updated: November 2026