Perimeter

Perimeter is the distance around a two-dimensional shape.


Imagine the distance to walk
all the way around the edge of a field.

Example: the perimeter of this rectangle is 7+3+7+3 = 20

Rectangle with length 7 and width 3 showing perimeter calculation

Example: the perimeter of this regular pentagon

Regular pentagon with all five sides labeled 3

3 + 3 + 3 + 3 + 3 = 5×3 = 15

circle

The perimeter of a circle is called the circumference:

Circumference = 2π × radius

Example: A circle has radius 4 cm, what's its circumference?

Using π ≈ 3.1416, and then rounded to 2 decimals:

Circumference = 2πr = 2π × 4 = 8π
≈ 25.13 cm

Perimeter Formulas

Triangle with sides labeled a, b, and c Triangle
Perimeter = a + b + c
Square Square
Perimeter = 4 × a
a = length of side
Rectangle with sides labeled a and b Rectangle
Perimeter = 2 × (a + b)
Quadrilateral Quadrilateral
Perimeter = a + b + c + d
circle Circle
Circumference = 2πr
r = radius
Sector Sector
Perimeter = r(θ+2)
r = radius
θ = angle in radians
ellipse Ellipse
Perimeter = very hard!

Try It Yourself

images/perimeter-ruler.js
625,626,757,3225,758,759,760,3224,3226,3227
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