How to Calculate Area of Shapes (With Formulas)
Published 2026-11-02
Area calculator is a top conversion-style search: flooring, paint, a garden bed, or a homework circle. Area is measured in square units — square feet, square meters, acres — not in feet.
Use the free tool
Run these formulas with your own numbers. Math stays in your browser.
Open Area Calculator →Our area calculator supports the common school shapes, including parallelograms and circular sectors. The triangle calculator solves a full triangle (sides and angles) when you need more than base × height / 2. The volume calculator is the 3-D version.
Open the area calculator
Choose a shape, enter the labeled sides or radius, pick a unit and read square feet plus other square units. Use the same linear unit for every input.
Formulas
A parallelogram uses base and height (the perpendicular height, not the slanted side). A circular sector uses the central angle in degrees: (θ/360) × πr². A triangle here is base and height; SSS/SAS/ASA live on the triangle calculator.
A = length × width
A = π × r²
A = (base × height) ÷ 2
A = base × height
A = (θ ÷ 360) × π × r²
Worked examples
A 10 ft by 10 ft rectangle is 100 square feet — the calculator’s default story.
A circle with radius 3 m is π × 9 ≈ 28.27 m². A 90° sector of that circle is a quarter of it, about 7.07 m².
| From | To | Notes |
|---|---|---|
| 1 acre | 43,560 sq ft | US survey acre in common use |
| 1 sq yd | 9 sq ft | 3 ft × 3 ft |
| 1 sq m | 10.7639 sq ft | exact enough for planning |
Rooms that are not rectangles
Split an L-shaped room into two rectangles and add. For paint, area is wall length × height minus windows if you measure them. Waste and pattern matching are extra — this page is geometry, not a contractor quote. “Area calculator” and “how to calculate area” are among the largest conversion-style searches because flooring is sold by the square foot and lots are discussed in acres. “Area of a circle” and “square footage calculator” are the same geometry with a different shape or unit.
- Pick the closest shape (or split the job into several).
- Measure each required length in one unit.
- Enter the values the shape asks for — sector needs the angle.
- Read square units, then convert if your store sells by the box.
- Open the triangle calculator if you know three parts of a triangle instead of base and height.
Use the free tool
Run these formulas with your own numbers. Math stays in your browser.
Open Area Calculator →Frequently Asked Questions
What is the difference between area and perimeter?
Area is the inside (square units). Perimeter is the outline (linear units).
Do I use diameter for a circle?
The calculator asks for what the shape form lists. Radius is half the diameter.
Why doesn’t parallelogram use the slanted side?
Height must be perpendicular to the base. The slanted side is longer than the height unless the angle is 90°.
Is a sector the same as a pizza slice?
Yes, in the school sense: a slice from the center with angle θ.
Can I get cubic volume here?
No. Use the volume calculator.
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