Percentages on chocolates can be confusing. The percentage refers to the amount of cacao in the chocolate. In general here are some chocolate guidelines:
Semi-sweet chocolate is generally in the range of 52% - 62% cacao.
Dark Chocolate is generally at least 62% cacao.
Bittersweet chocolate is usually in the range of 63% - 72% cacao. It can go up to as high as 99%, however this is not a range of chocolate that people are generally comfortable eating.
Milk chocolate, which as the name implies is chocolate to which milk has been blended, will be lablled in the 40% range. It can go as low as 36% cacao.
White chocolate, which also contains milk, is eichincally not chocolate. This is because white coacoalte does not contain cacao solids. However, it is made with cocoa butter.