📏 Geometry Calculator
Calculate area and perimeter for any 2D shape. Select a shape, enter the required dimensions, and get instant results with the formula used.
How to Use
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1Select a ShapeChoose from the dropdown: circle, rectangle, square, triangle, trapezoid, parallelogram, ellipse, or rhombus.
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2Enter DimensionsFill in the required measurements. The input fields update automatically when you change shape.
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3Click CalculateInstantly see the area and perimeter (or circumference) with the formula used.
Example — Circle with r = 7
Frequently Asked Questions
Area measures the surface covered inside a shape (in square units), while perimeter measures the total length of the boundary around the shape (in linear units). For a circle, the perimeter is called the circumference.
The most common formula is Area = ½ × base × height. If you know all three sides (a, b, c) but not the height, use Heron's formula: s = (a+b+c)/2, Area = √(s(s−a)(s−b)(s−c)).
Pi (π) is the ratio of a circle's circumference to its diameter. It is approximately 3.14159265. It appears in all formulas involving circles and ellipses.
The perimeter of a circle is called the circumference. It equals 2πr (where r is the radius) or πd (where d is the diameter).
For an ellipse with semi-axes a and b, the perimeter ≈ π × [3(a+b) − √((3a+b)(a+3b))]. This is much more accurate than the simple approximation π(a+b) and is the formula used in this calculator.
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