in = mm / 25.4,
cmm = PI * ( mm / 2 )2,
cin = PI * ( mm / 50.8)2,
Where,
in is the size of the wire in inches,
mm is the size of the wire in mm,
cmm is the cross sectional area in mm,
cin is the cross sectional area in inches.
The value of mm is found from this
Calculator 
Formula 
