Area Calculator for Rectangles, Triangles, Circles and More
Pick a shape, enter its measurements in one unit, and get the area in that unit squared, converted to square feet, square meters, acres and more.
Area is the space inside a flat shape, measured in square units. A rectangle is length times width, so a room 12 feet by 10 feet is 120 square feet. A triangle is half of base times height, a circle is pi times the radius squared, and a trapezoid is the average of its two parallel sides times the height between them. A circle with a 5 foot radius covers about 78.54 square feet.
This calculator assumes ideal geometric shapes measured in one unit. It does not account for irregular edges, wall thickness, slopes or material waste, and it is not a land survey. Measure carefully and add a waste allowance when buying flooring, paint or other materials.
Area
120 sq ft
- Square inches
- 17,280
- Square feet
- 120
- Square yards
- 13.3333
- Square meters
- 11.1484
- Square centimeters
- 111,483.648
- Acres
- 0.0028
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About the Area Calculator
Every area formula counts how many unit squares fit inside a shape. For a rectangle that is simply rows times columns, which is why length times width works. A triangle is half of the rectangle drawn around it, so it is base times height, halved, where the height is measured straight up from the base, not along a slanted side. When you only know the three sides, Heron's formula works it out: add the sides and halve the total to get s, then take the square root of s times s minus each side. Sides of 7, 8 and 9 give about 26.83 square units. The three sides must pass the triangle test, with any two adding up to more than the third, or the shape cannot close. A circle is pi times the radius squared, an ellipse is pi times its two half-widths, and a sector, the pie slice, is the circle's area times the angle over 360 degrees. Enter every measurement in the same unit; the answer comes out in that unit squared and is then converted, so 120 square feet also shows as about 11.15 square meters and 13.33 square yards.
Frequently asked questions
How do I find the area of a room in square feet?+
Measure the length and width in feet and multiply: 12 x 10 = 120 square feet. For an L-shaped room, split it into two rectangles, find each area, and add them. If you measured in inches, divide the square inches by 144 to get square feet.
What if I only know the three sides of a triangle?+
Choose the three-sides option, which uses Heron's formula. For sides 7, 8 and 9 the half-perimeter is 12, and the area is the square root of 12 x 5 x 4 x 3 = 720, about 26.83. Very thin triangles lose some precision, so a base and a measured height is better when you have them.
Can I mix feet and inches?+
No. Convert everything to one unit first, so 10 feet 6 inches becomes ten and a half feet, or 126 inches. The calculator treats every box as the unit you picked, and only the finished area is converted to other units.
How many square feet are in an acre?+
An acre is exactly 43,560 square feet, a little over 4,046 square meters. The calculator uses the international foot. Older US land surveys use the survey foot, whose acre is larger by about 2 parts per million, a difference that matters only on an official land survey.
How is the area of a circle calculated from its diameter?+
Halve the diameter to get the radius, then multiply pi by the radius squared. A 10 foot circle has a 5 foot radius, so its area is about 78.54 square feet.
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