Area formulas for common shapes
Area measures the two-dimensional space inside a shape, always in square units (cm², m², ft²). Each shape has its own formula:
rectangle: A = length × width
circle: A = π × radius²
triangle: A = ½ × base × height
trapezoid: A = ½ × (a + b) × height
parallelogram: A = base × height
Worked example
Area of a circle with radius 5:
Square the radius: 5² = 25.
Multiply by π: 25 × 3.14159… ≈ 78.54 square units.
Units and tips
All inputs must use the same unit; the result is in that unit squared. For a square, enter the same value for length and width. For irregular shapes, split them into the shapes above, find each area, and add the results together.
Tip: the triangle formula here uses base and height. If you only know the three side lengths, use Heron's formula instead — but the perpendicular height is the most common case.