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.
Perimeter Result:
On this page:
- Perimeter Calculator
- How to Find the Perimeter of a Shape
- Perimeter Formulas
- Square Perimeter Formula
- Rectangle Perimeter Formula
- Trapezoid Perimeter Formula
- Parallelogram Perimeter Formula
- Rhombus Perimeter Formula
- Triangle Perimeter Formula
- Circle Perimeter Formula
- Ellipse Perimeter Formula
- Sector Perimeter Formula
- Sector Perimeter Formula
- Pentagon Perimeter Formula
- Hexagon Perimeter Formula
- Octagon Perimeter Formula
- Regular Polygon Perimeter Formula
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
Rectangle Perimeter Formula
P = 2l + 2w
l = length
w = width
Trapezoid Perimeter Formula
P = a + b + c + d
a = base a
b = base b
c = side c
d = side d
Parallelogram Perimeter Formula
P = 2a + 2b
a = side
b = base
Rhombus Perimeter Formula
P = 4a
a = edge length
Triangle Perimeter Formula
P = a + b + c
a = edge a
b = edge b
c = edge c
Circle Perimeter Formula
P = 2πr
r = radius
Try our circumference calculator to solve using the radius, diameter, or area.
Ellipse Perimeter Formula
P ≈ π[3(a + b) – (((3a + b))(a + 3b))]
a = axis a
b = axis b
Sector Perimeter Formula
P = 2r + ((2θπr) ÷ 360)
r = radius
θ = angle in degrees
Sector Perimeter Formula
P = πrθ / 180 + 2r × sin(θ / 2)
r = radius
θ = angle in degrees
Pentagon Perimeter Formula
P = 5a
a = edge length
Hexagon Perimeter Formula
P = 6a
a = edge length
Octagon Perimeter Formula
P = 8a
a = edge length
Regular Polygon Perimeter Formula
P = an
a = edge length
n = number of sides
To find the area of these shapes, try our area calculator.