What is the formula for the mean diameter of the magnet coils?

• A. mean diameter = inside diameter of coil + outer diameter of coil / 2
• B. mean diameter = inside diameter of coil ‚Äö√Ñ√∂‚àö√ë‚àö¬® outer diameter of coil / 2
• C. mean diameter = inside diameter of coil * outer diameter of coil / 2
• D. mean diameter = inside diameter of coil / outer diameter of coil / 2