What is Video Class?
Video Speed Class is a performance rating from the SD Association, printed on SD and microSD cards as a stylized V followed by a number: V6, V10, V30, V60 or V90. The number is the card's guaranteed minimum sustained write speed in megabytes per second. A V30 card can keep writing at least 30 MB/s, which is what a camera, drone or dashcam needs while it records a continuous video stream. If the card can't keep up, recording stops or frames are dropped.
Don't confuse it with USB Video Class (UVC), the standard that lets webcams work with the operating system's built-in driver.
The three speed ratings on SD cards
| Rating | Markings | Minimum sustained write |
|---|---|---|
| Speed Class | C2, C4, C6, C10 (number inside a C) | 2, 4, 6 or 10 MB/s |
| UHS Speed Class | U1, U3 (number inside a U) | 10 or 30 MB/s |
| Video Speed Class | V6, V10, V30, V60, V90 | 6, 10, 30, 60 or 90 MB/s |
The ratings overlap, so one card often carries several marks. A card marked C10, U3 and V30 guarantees at least 30 MB/s; the C10 mark alone only promises 10. Video Speed Class was added to cover the higher sustained speeds that 4K and 8K recording need.
Markings that aren't speed classes
- UHS-I, UHS-II, UHS-III (Roman numerals): the bus interface. UHS-II and UHS-III cards have a second row of contacts and need a matching host to reach full speed.
- A1, A2: Application Performance Class, for the random reads and writes of apps running from the card, as on phones and tablets.
- "Up to" MB/s figures: the large number on the label is usually a peak speed, often for reads, not the guaranteed sustained write.
- SDHC, SDXC: capacity types, which decide compatibility with the host, not speed.
Choosing a card
Start with the device manual, which usually states the minimum class for each recording mode. As a rule of thumb, basic HD recording works with C10, U1 or V10, many 4K modes call for U3 or V30, and high-bitrate or 8K modes may need V60 or V90. Photos and general storage rarely need a fast class. Buy from reliable sellers: counterfeit cards can carry speed marks they can't meet and may even report more capacity than they hold.
For the CompTIA A+ exam
Core 1 (220-1201) objective 3.4 lists memory cards under removable storage. Video Speed Class isn't named, but card markings come up in practical scenarios: if a camera stops recording or drops frames at a high-resolution setting, check that the card's speed class meets the device's requirement before blaming the camera.