You need 21 of the the 121 merit badges to be Eagle, but there are 12 REQUIRED merit badges.
Of the 21 merit badges, 12 are REQUIRED for Eagle Scout; these include:
- First Aid
- Citizenship in the Community
- Citizenship in the Nation
- Citizenship in the World
- Personal Fitness
- Environmental Science
- Personal Management
- Family Life
- Emergency Preparedness or Lifesaving
- Swimming or Hiking or Cycling.
NOTE 1: Sustainability merit badge will be introduced at the 2013 National Jamboree as an alternative to Environmental Science merit badge.
NOTE 2: Cooking merit badge will be revised and required as of January 1, 2014, bringing the total required to 13