Socks can stretch; one size can fit multiple lengths while shoes are rigid, so sizing shoes requires many more options on a shoe size chart. In the U.S., sock sizes can be described by the length of the foot in inches or matching a shoe size to the corresponding sock.
For the most part, sizes are not exactly the same for both socks and shoes for girls, boys or adults. Girls' U.S. shoe sizes from 00 to 4 1/2 have corresponding sock sizes that are higher than the shoe size. For girls' U.S. shoe sizes 5 to 13 1/2, the appropriate sock size is the same size or higher.
Sock packaging or store employees can help match the precise girls shoe size to its appropriate sock size. As girls grow, their shoe sizes will change more frequently than their sock sizes because socks can stretch to a certain extent.
Manufacturers in each country typically use their own unique sizing systems. Check the product information to see if socks are sized according to U.S. sizes or some other country's sizes. Specialty shops in the U.S. selling imported clothing and online retailers shipping directly from overseas may sell socks sized for other countries.