How you draw/calculate the anchor swinging circle?

Ship’s length (Bridge GPS antenna to fwd) + (How many shackles x 27.5m)

FOR Example :
=   6 shackle on deck and (bridge GPS antenna to fwd) is indicated by L = 100m
=   6 shackle +L
=     6×27.5m +100
=    265m
=     (265/ 1854 ) nm
= 0.1431nm
=   (0.1431×10) cable  @ one NM is equal to 10 cable
=    1.431 cable

Note :
Centre of swinging circle is the point where anchor fluke touches SEABED.

Alternatively, The following is the formula used to calculate Swing Radius of a boat at anchor.:   

 Swing Radius = LOA + [ ( RODE ) 2 – ( DEPTH + FREEBOARD)2 ] 1/2

LOA:  Overall length of the boat, including any additions or extensions from the stern
RODE:  The length (line to the anchor) of the rode from the bow pulpit to the anchor.
DEPTH:  The water depth over the anchor.
FREEBOARD:  The distance from the deck at the bow pulpit to the water.