The square which is made in a circle such that all four vertices of a square touches circle is called Circumscribed square.

By Pythagoras theorem in triangle BOC
s2 = r2 + r2
s = √2r
Areas | In terms of radius ‘r’ | In terms of side ‘s’ |
Area of square ABCD with side ‘s’ | 2 r2 | s2 |
Area of circle with radius ‘r’ | ∏ r2 | ∏ s2 /2 |