Perimeter Calculator

Calculate the perimeter of 9 different shapes including triangles, circles, polygons, trapezoids, and ellipses. Change the shape to automatically update the required fields and see the geometry graphic on the right.

Select Shape

Perimeter Formulas

Square

P = 4 × side

Rectangle

P = 2 × (L + W)

Triangle

P = a + b + c

Circle

P = 2πr

Parallelogram

P = 2 × (base + side)

Trapezoid

P = a + b + c + d

Rhombus

P = 4 × side

Regular Polygon

P = n × side

Ellipse (Ramanujan Approx)

P ≈ π [3(a + b) – √((3a+b)(a+3b))]

Frequently Asked Questions

Yes — circumference is simply perimeter of a circle.

Because no exact closed formula exists for ellipse perimeter.