Original: Regulations also govern what may be marketed as "white chocolate": In the United States, since 2004, white chocolate must be at least 20% cocoa butter (by weight), at least 14% total milk solids, at least 3.5% milk fat, and less than 55% sugar or other sweeteners.
Simplified: In the United States, white chocolate must be at least 20% cocoa butter, at least 14% total milk solids, at least 3.5% milk fat, and less than 55% sugar or other sweeteners.