Developed Length of Bends

as published in a Pro-Engineer sheet metal manual.
               L=((pi/2) x R + yfactor x T) x (A/90)

		 L= Developed length.
		 R= Inside bend radius.
		 yfactor= .5 (A constant defined by 
		   the location of the neutral bend line).
		 T= Material thickness.
		 A= Bend angle.

For a different formula and a sheet metal bend calculator try