What is the formula for depth of winding of the magnet coils?

• A. depth of winding = mean diameter of coil ‚Äö√Ñ√∂‚àö√ë‚àö¬® inner diameter
• B. depth of winding = mean diameter of coil + inner diameter
• C. depth of winding = mean diameter of coil ‚Äö√Ñ√∂‚àö√ë‚àö¬® 2* inner diameter
• D. depth of winding = mean diameter of coil + 2*inner diameter