Diagonal of a square calculator

The diagonal of a square is the line segment joining two opposite corners. It divides the square into two right-angled triangles: the two shorter sides of each triangle are sides of the square, and the diagonal itself is their hypotenuse. The diagonal is always about 1.41 times as long as the side.

How it works

By Pythagoras’ theorem, the diagonal of a square with side a is

$$d=\sqrt{a^2+a^2}=\sqrt{2a^2}=a\sqrt{2}$$

A square with a side of 5 cm has a diagonal of about 7.07 cm.

For the diagonals of other shapes, use the calculators for the diagonal of a rectangle, cube and cuboid.