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

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

Calculate square perimeter

Diagram of a square showing a = edge length

Rectangle Perimeter Formula

P = 2l + 2w

l = length
w = width

Calculate rectangle perimeter

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

Calculate trapezoid perimeter

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

Calculate parallelogram perimeter

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

Calculate triangle perimeter

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

Circle Perimeter Formula

P = 2πr

r = radius

Calculate circumference of a circle

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

Calculate circumference of an ellipse

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

Sector Perimeter Formula

P = 2r + ((2θπr) ÷ 360)

r = radius
θ = angle

Calculate sector perimeter

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

Regular Polygon Perimeter Formula

P = an

a = edge length
n = number of sides

Calculate regular polygon perimeter

Diagram of a regular polygon showing a = edge length

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