
Start with the given circle, center O.
If the circle center point is not given, you can construct the center using the method shown in
Finding the center of a circle. 

1 
Mark a point A on the circle. This will become one of the vertices of the square. 

2 
Draw a diameter line from the point A, through the center and on to cross the circle again, creating point C. 

3 
Set the compass on A and set the width to a little more than the distance to O. 

4 
Draw an arc above and below O. 

5 
Move the compass to C and repeat. 

6 
Draw a line through where the arc pairs cross, making it long enough to touch the circle at top and bottom,
creating the new points B and D.
This is a diameter at right angles to the first one AC. 

7 
Draw a line between each successive pairs of points A, B, C, D 


Done. ABCD is a square inscribed in the given circle. 
