Diagonals of a rectangle

A rectangle has two diagonals, which are line segments linking opposite vertices (corners) of the rectangle.
Try this Drag any vertex of the rectangle below. It will remain a rectangle and the length of the diagonal will be calculated.

A rectangle has two diagonals. Each one is a line segment drawn between the opposite vertices (corners) of the rectangle. The diagonals have the following properties:

Length of the diagonal

In the figure above, click 'reset'. As you can see, a diagonal of a rectangle divides it into two right triangles, BCD and DAB. The diagonal of the rectangle is the hypotenuse of these triangles. We can use Pythagoras' Theorem to find the length of the diagonal if we know the width and height of the rectangle.

As a formula: where:
w  is the width of the rectangle
h  is the height of the rectangle


Side 1 clear
Side 2 clear

Use the calculator above to calculate the properties of a rectangle.

Enter the two side lengths and the rest will be calculated. For example, enter the two side lengths. The area, perimeter and diagonal lengths will be found.

Things to try

  1. In the figure at the top of the page, click on 'reset' and 'hide details'. Then drag the corners to create an arbitrary rectangle. Calculate the length of the diagonals. Click 'show details' to verify your answer.
  2. A rectangle has a height of 12 and a diagonal of 31. Find the width of the rectangle and use the animation or the calculator above to verify your answer.

Other polygon topics


Types of polygon

Area of various polygon types

Perimeter of various polygon types

Angles associated with polygons

Named polygons