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Perimeter Calculator

Find the perimeter of a rectangle, square, triangle, circle, trapezoid, parallelogram, rhombus, ellipse, sector, segment or regular polygon.

Change the values and press Calculate to work out your own figures.

Rectangle

Enter the length and width.

The longer side.
The shorter side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the rectangle
100 ft
Area
600 ft²

The perimeter of the rectangle is 100 ft.

Show the working
  1. P = 2(l + w)
  2. Perimeter = 100 ft

Square

Enter the side.

The length of a side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the square
48 ft
Area
144 ft²

The perimeter of the square is 48 ft.

Show the working
  1. P = 4a
  2. Perimeter = 48 ft

Triangle

Enter the side a, side b and side c.

First side.
Second side.
Third side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the triangle
125 ft
Area
666.5852815 ft²

The perimeter of the triangle is 125 ft.

Show the working
  1. P = a + b + c
  2. Perimeter = 125 ft

Circle

Enter the radius.

From the centre to the edge.
The unit of every measurement; the answer is then also given in other units.
Result
Circumference of the circle
62.83185307 ft
Exact
20π ft
Diameter
20 ft

The circumference of the circle is 62.83185307 ft (20π ft).

Show the working
  1. C = 2 π r
  2. Circumference = 62.83185307 ft

Trapezoid

Enter the base a, base b, side c and side d.

One of the parallel sides.
The other parallel side.
Third side.
Fourth side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the trapezoid
75 ft

The perimeter of the trapezoid is 75 ft.

Show the working
  1. P = a + b + c + d
  2. Perimeter = 75 ft

Parallelogram

Enter the side a and side b.

First side.
Second side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the parallelogram
100 ft

The perimeter of the parallelogram is 100 ft.

Show the working
  1. P = 2(a + b)
  2. Perimeter = 100 ft

Rhombus

Enter the side.

The length of a side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the rhombus
52 ft

The perimeter of the rhombus is 52 ft.

Show the working
  1. P = 4a
  2. Perimeter = 52 ft

Ellipse (oval)

Enter the semi-axis a and semi-axis b.

Half the width (horizontal).
Half the height (vertical).
The unit of every measurement; the answer is then also given in other units.
Result
Circumference of the ellipse
158.6543959 ft
Ramanujan's approximation
158.6543758 ft

The circumference of the ellipse is 158.6543959 ft.

Show the working
  1. C = 4a E(e), the complete elliptic integral, worked out exactly by the arithmetic–geometric mean
  2. Circumference = 158.6543959 ft

Sector

Enter the radius and angle.

From the centre to the edge.
The angle, in the unit chosen below.
Degrees or radians.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the sector
107.1238898 ft
Arc length
47.1238898 ft (15π)
Sector area
706.8583471 ft² (225π)

The perimeter of the sector is 107.1238898 ft.

Show the working
  1. P = 2r + arc length
  2. Perimeter = 107.1238898 ft

Circular segment

Enter the radius and angle.

From the centre to the edge.
The angle, in the unit chosen below.
Degrees or radians.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the circular segment
20.47197551 ft
Arc length
10.47197551 ft (10π/3)
Chord length
10 ft
Segment area
9.058607371 ft²

The perimeter of the circular segment is 20.47197551 ft.

Show the working
  1. P = arc length + chord length
  2. Perimeter = 20.47197551 ft

Regular polygon

Enter the number of sides and side.

3 to 1,000.
The length of a side.
The unit of every measurement; the answer is then also given in other units.
Result
Perimeter of the regular polygon
40 ft
Area (A)
120.7106781 ft²
Circumradius (R)
6.532814824 ft
Inradius (r)
6.035533906 ft
Long diagonal (d)
13.06562965 ft
Medium diagonal (m)
12.07106781 ft
Short diagonal (s)
9.238795325 ft
Interior angle
135°

The perimeter of the regular polygon is 40 ft.

Show the working
  1. P = n × a
  2. Perimeter = 40 ft

How to use it

Enter the length and width. Enter the side. Enter the side a, side b and side c. Enter the radius. Enter the base a, base b, side c and side d. Enter the side a and side b. Enter the side. Enter the semi-axis a and semi-axis b. Enter the radius and angle. Enter the radius and angle. Enter the number of sides and side.

Enter the measurements (decimals, fractions such as 3/4, or mixed numbers such as 1 1/2) and, if you like, their unit; the answer is then also given in other units. Show the working gives the formula.

Key facts

Rectangle P = 2(l + w); circle C = 2πr; regular polygon P = n a

The ellipse's perimeter

There is no simple formula for the distance around an ellipse. The calculator evaluates the exact value (a complete elliptic integral) with the arithmetic–geometric mean; Ramanujan's approximation agrees to within a few parts per billion for most ellipses.

Questions

What is the perimeter of a 30 × 20 rectangle?

100.

What is the circumference of a circle of radius 10?

20π ≈ 62.83185307.

Reviewed by RK Calculator Team. Updated 2026-09-26.

Formulas

Rectangle P = 2(l + w); circle C = 2πr; regular polygon P = n a

Sources

Limitations

  • All measurements in one calculation use the same unit; the answer is also given in other units.
  • Measurements up to 10¹⁵.

Formula version 0.1.0Reviewed