Perimeter Calculator

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

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

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How to Find the Perimeter of a Shape

Perimeter is the length of the outer edge or boundary of a two-dimensional shape and is expressed in units of length, such as inches or feet. The word perimeter is actually derived from the Greek words peri (‘around’) and metron (‘measure’), meaning a measurement around something.

Since perimeter is the total boundary length, it is equal to the sum of the edge lengths for polygons with multiple edges.

So, you can find the perimeter of any polygon by measuring each edge of the shape and adding the edge lengths together to get the total length. For instance, for a rectangle, the perimeter is equal to the length plus the length plus the width plus the width.

For shapes with curved edges, such as a circle or ellipse, the perimeter is referred to as the circumference, and you’ll need a formula to find it.

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

Perimeter Formulas

Each shape has a unique formula for its perimeter; see the formulas for the most common shapes below.

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

Rhombus Perimeter Formula

P = 4a

a = edge length

Diagram of a rhombus showing a = edge length

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 in degrees

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

Sector Perimeter Formula

P = πrθ / 180 + 2r × sin(θ / 2)

r = radius
θ = angle in degrees

diagram of a circular segment showing the radius, central angle, chord length, height, and arc length

Pentagon Perimeter Formula

P = 5a

a = edge length

Diagram of a pentagon showing a = edge length

Hexagon Perimeter Formula

P = 6a

a = edge length

Diagram of a hexagon showing a = edge length

Octagon Perimeter Formula

P = 8a

a = edge length

Diagram of a octagon showing a = edge length

Regular Polygon Perimeter Formula

P = an

a = edge length
n = number of sides

Diagram of a regular polygon showing a = edge length

To find the area of these shapes, try our area calculator.