What is Perimeter?
In geometry, the perimeter is the total path or distance that surrounds a two-dimensional shape. For shapes with straight sides (polygons), it is the sum of all side lengths. For curved shapes like circles, this distance is specifically called the circumference.
[Image of perimeter vs area diagram showing the boundary highlight vs the internal space]Common Perimeter Formulas
Our calculator utilizes these standard geometric proofs to ensure 100% accuracy:
Rectangle
$P = 2 \times (length + width)$
Circle (Circumference)
$C = 2 \times \pi \times r$
Triangle
$P = a + b + c$
Real-World Applications
Understanding perimeter isn't just for math class. It is a vital calculation in several professional fields:
- Construction & Fencing: Determining how many linear feet of fencing are required to enclose a yard.
- Interior Design: Calculating the amount of crown molding or baseboards needed for a room.
- Graphics & Design: Setting the "stroke" or border thickness around digital elements.
The Case of the Ellipse
Unlike a circle, calculating the perimeter (circumference) of an ellipse is surprisingly complex. There is no simple exact formula. Our tool uses Ramanujan's Approximation for the most precise result possible:
$P \approx \pi [3(a+b) - \sqrt{(3a+b)(a+3b)}]$
2026 Math Tip: Always ensure your units are consistent (e.g., all inches or all centimeters) before calculating. If you mix units, the resulting perimeter will be incorrect!