The Speed Class Rating is the official unit of speed measurement for SD Cards, defined by the SD Association. The Class number represents a multiple of 8 Mbit/s (1 MB/s), the least sustained write speeds for a card in a fragmented state (Class 2, 4, 6) or the minimum non-fragmented sequential write speed (Class 10).
These are the ratings of all currently available cards:
Class 2 - 2 MB/s
Class 4 - 4 MB/s
Class 6 - 6 MB/s
Class 10 - 10 MB/s
The Northern Monkey wrote:
are the standards for a card to be called class 4/6/10 by law/legislation or is it different between manufacturers?