How to Read SD Card Speed Classes

Decode SD card labels, speed classes, and symbols to ensure you purchase the correct storage for 4K video, burst photography, and high-speed data transfers.

1. Locate the Speed Class (C) symbol. Look for the letter 'C' with a number inside it on the SD card label. This represents the legacy Speed Class, indicating the minimum sustained write speed in MB/s. A 'C10' rating denotes a minimum write speed of 10MB/s, suitable for standard video recording.
2. Check the UHS Speed Class (U) symbol. Identify the letter 'U' containing either a '1' or a '3'. U1 guarantees a minimum write speed of 10MB/s, while U3 guarantees 30MB/s, which is the baseline requirement for 4K video recording at 30fps.
3. Find the Video Speed Class (V) rating. Locate the 'V' symbol followed by a number, such as V6, V30, or V90. This indicates the card's ability to handle high-bitrate video; V60 and V90 are required for 8K video capture. Match the number directly to the MB/s sustained write speed requirement of your camera.
4. Identify the UHS Bus Interface. Search for Roman numerals 'I', 'II', or 'III' on the card. This denotes the physical bus speed, where UHS-II and UHS-III cards feature an extra row of pins on the back. Ensure your device hardware supports these physical pins, or the card will revert to standard UHS-I speeds.
5. Confirm the Application Performance Class (A). Look for the 'A' symbol followed by '1' or '2'. This indicates the card is optimized for mobile applications and random read/write operations. A2-rated cards provide better performance for running apps directly from microSD cards in smartphones or handheld consoles.