SD Card classes

SD Card classes

SD Card classes designate the minimum write speed of the flash memory for recording video. Starting in 2010, the Ultra High Speed (UHS) bus was introduced, dramatically increasing bus speeds from a maximum of 25 to 104 Mbytes/sec (UHS-I) and later to 312 Mbytes/sec (UHS-II). UHS host devices also support non-UHS memory cards at the lower speeds. See SD Card.

 Speed  Bus     Minimum Class  Type    MB/sec  Recording

  C2    Normal     2      SD
  C4    Normal     4      HD
  C6    Normal     6      HD
  C10   High-     10    Consecutive
         Speed           recording of
                         HD stills
 UHS Speed Class

  U1    UHS-I/II  10      HD
  U3    UHS-I/II  30      4K

Class Marks
Ratings are encapsulated in a "C" for class and a "U" for UHS. The Roman numeral II is the UHS-II bus. (Image courtesy of SD Association,

UHS-II SD and microSD
UHS-II cards have a second row of pins for UHS-II signals. The original row near the edge remain the normal, high-speed and UHS-I interfaces. (Image courtesy of SD Association,