Turn the round table upside down on a flat surface.
Draw two straight lines on the bottom of the table diagonally from one corner leg through the other to form an X.
Extend the line through the legs to the edge of the table.
The spots where each line reaches the edge of the table are the corner points of the square.
Draw four straight lines to connect these corner points to form the square.
If the legs are flush with the edge of the table, they can be removed and repositioned to allow for the desired overhang.
Use the saw to cut along the four straight lines that form the square.
Sand the edges and finish them to match the finish on the tabletop, or finish the edges with another color for contrast.