Memory card speed classes tell you the minimum sustained write speed a card is designed to hold, and the right one depends mostly on whether you shoot stills in bursts or record high-bitrate video. The labels look confusing, but a few symbols cover almost everything you will see on an SD card.
The Main Symbols
SD cards carry several overlapping markings. Each one covers a different idea, so check which ones your camera needs.
- Speed Class (C2, C4, C6, C10): The number is the minimum sustained write speed in megabytes per second. Class 10 means 10 MB/s.
- UHS Speed Class (U1, U3): U1 means at least 10 MB/s and U3 means at least 30 MB/s.
- Video Speed Class (V6, V10, V30, V60, V90): The number again is the minimum sustained write speed, so V30 means 30 MB/s and V90 means 90 MB/s.
- UHS bus (UHS-I, UHS-II): This describes the interface. UHS-II cards have an extra row of pins and can transfer faster when the camera supports it.
Do not confuse the minimum sustained speed with the maximum read speed printed in large type on the front. The big number is a best case for transferring files to a computer, not a promise for recording.
Quick Reference
| Label | Minimum sustained write | General use |
|---|---|---|
| Class 10 / U1 / V10 | 10 MB/s | Basic stills, standard HD video |
| U3 / V30 | 30 MB/s | 4K video, burst stills |
| V60 | 60 MB/s | Higher bitrate 4K |
| V90 | 90 MB/s | Very high bitrate video, 8K |
How to Match a Card to Your Camera
- Check your camera’s manual for the card type, bus support and any recommended video class.
- Look at the highest video bitrate you plan to record, and choose a class with a comfortable margin.
- For fast burst shooting in RAW, favor a card with a higher sustained write speed so the buffer clears sooner.
- Confirm the card format your camera uses, since some bodies use CFexpress or XQD instead of SD.
- Buy from authorized sellers, since counterfeit cards do exist.
Practical Tips
Format the card in the camera, not on a computer, to keep the file system clean. Carry more than one smaller card rather than putting everything on a single large one. Use a quality reader for transfers, and avoid pulling a card while the camera is writing.
FAQ
Will a faster card improve my image quality?
No. Speed affects how quickly data is written, not how the picture looks. A faster card helps with burst length and video bitrate limits.
Can I use a UHS-II card in a UHS-I camera?
Usually yes, because the cards are backward compatible, but you will only get UHS-I speeds.
The Short Version
Read the minimum sustained write number, not the big read speed. U3 and V30 handle most 4K and burst needs, and V60 or V90 suit demanding video. Confirm your camera’s requirements in its manual.
