Perimeter Calculator

Calculate the perimeter of a shape by selecting a shape and entering your measurements in any unit, metric or imperial. See formulas for each shape below.

Select a Shape:

Rectangle Perimeter Calculator

Square Perimeter Calculator

Trapezoid Perimeter Calculator

Parallelogram Perimeter Calculator

Triangle Perimeter Calculator

Circle Circumference Calculator

Ellipse Circumference Calculator

Sector Perimeter Calculator

Regular Polygon Perimeter Calculator



How to Find the Perimeter of a Shape

Perimeter is the length of the outer edge or boundary of a 2-dimensional shape and is expressed in units of length, such as inches or feet. Perimeter is often found by measuring each edge of a shape and adding the edge lengths together to get the total length. The outer edge of a circle or ellipse is referred to as the circumference.

When measuring use the same unit of measurement for each edge, and use our length unit conversion calculators to convert all measurements to the same length if needed.


Square Perimeter Formula

P = 4a

a = edge length

Diagram of a square showing a = edge length

Rectangle Perimeter Formula

P = 2l + 2w

l = length
w = width

Diagram of a rectangle showing l = length and w = width

Trapezoid Perimeter Formula

P = a + b + c + d

a = base a
b = base b
c = side c
d = side d

Diagram of a trapezoid showing a = base a, b = base b, c = side c, and d = side d

Parallelogram Perimeter Formula

P = 2a + 2b

a = side
b = base

Diagram of a parallelogram showing a = side and b = base

Triangle Perimeter Formula

P = a + b + c

a = edge a
b = edge b
c = edge c

Diagram of a triangle showing a = edge a, b = edge b, and c = edge c

Circle Perimeter Formula

P = 2πr

r = radius

Try our circumference calculator to solve using the radius, diameter, or area.

Diagram of a circle showing r = radius

Ellipse Perimeter Formula

P ≈ π[3(a + b) – (((3a + b))(a + 3b))]

a = axis a
b = axis b

Diagram of an ellipse showing a = axis a and b = axis b

Sector Perimeter Formula

P = 2r + ((2θπr) ÷ 360)

r = radius
θ = angle

Diagram of a sector showing r = radius and θ = angle

Regular Polygon Perimeter Formula

P = an

a = edge length
n = number of sides

Diagram of a regular polygon showing a = edge length

Use our area calculator to find the area of a shape.