How do I convert between area units?

Square the linear conversion factor. Since 1 foot = 12 inches, 1 sq ft = 144 sq in. Since 1 meter = 100 cm, 1 sq m = 10,000 sq cm. For acres, 1 acre = 43,560 sq ft.

What is the area of a circle with diameter instead of radius?

Divide the diameter by 2 to get the radius, then use A = π × r². Alternatively, use A = π × d² / 4 directly with the diameter.

How do I find the area of an irregular shape?

Break the irregular shape into standard shapes (rectangles, triangles, etc.), calculate each area separately, then add them together. This decomposition method works for most practical shapes.

What is the difference between area and perimeter?

Area measures the surface inside a shape (in square units). Perimeter measures the distance around the outside edge (in linear units). A 5×3 rectangle has area = 15 sq units and perimeter = 16 units.

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Area Calculator

Calculate the area of common geometric shapes including rectangles, triangles, circles, trapezoids, ellipses, and parallelograms.

Length

Width

Quick Facts

Most common shape (architecture)Rectangle

π approximation3.14159...

1 acre in sq ft43,560

1 hectare in sq m10,000

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Percentage Calculator

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How to Use This Calculator

Select a shape from the grid: rectangle, triangle, circle, trapezoid, ellipse, or parallelogram.
Enter the required dimensions for your chosen shape.
Click Calculate to see the area, formula, and explanation.

The Formula

Rectangle: A = length × width. Triangle: A = ½ × base × height. Circle: A = π × radius². Trapezoid: A = ½ × (base₁ + base₂) × height. Ellipse: A = π × a × b. Parallelogram: A = base × height.

Frequently Asked Questions

The rectangle formula (length × width) is the most commonly used in everyday life — for rooms, lots, screens, and paper sizes. Most other shapes can be approximated or decomposed into rectangles.