MicroSD Card Speed Classes, Explained
The C, U and V symbols on a microSD card each promise a minimum write speed in MB/s; U3 and V30, for example, both mean at least 30 MB/s.
By Liam McCabeContributing writer.
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The short answer
The small symbols printed on a microSD card are speed classes. Each one is a promise from the SD Association's standard: the card can keep writing at least that many megabytes per second (MB/s) under the test conditions in the standard. That steady minimum is what video recording needs, because a camera that cannot write fast enough drops frames.
There are four families of symbols, and the number inside each one is the speed:
- Speed Class: a C with a number (2, 4, 6 or 10).
- UHS Speed Class: a U with 1 or 3.
- Video Speed Class: a V with 6, 10, 30, 60 or 90.
- SD Express Speed Class: an E with 150, 300, 450 or 600.
Speed classes and minimum write speed
This table follows the SD Association's speed class chart.
| Minimum write speed | Speed Class | UHS Speed Class | Video Speed Class |
|---|---|---|---|
| 2 MB/s | C2 | ||
| 4 MB/s | C4 | ||
| 6 MB/s | C6 | V6 | |
| 10 MB/s | C10 | U1 | V10 |
| 30 MB/s | U3 | V30 | |
| 60 MB/s | V60 | ||
| 90 MB/s | V90 |
The same chart lines the speeds up with video formats: standard and HD video sit toward the slow end, 4K in the middle and 8K at the top. The SD Association adds that the speed you need depends on the recording device, so the device's manual is the final word.
The SD Express classes (150 to 600 MB/s) need a card and device with the SD Express interface.
V30 vs U3
On paper, V30 and U3 promise the same thing: at least 30 MB/s. The difference is age. The SD Association says the older Speed Class and UHS Speed Class were tuned for older flash memory, while Video Speed Class was written for 4K and 8K recording and newer 3D NAND flash. Many cards carry both symbols.
Two rules from the SD Association help you pick:
- Match or beat the device's symbol. If a camera asks for U1, a U1 or U3 card works. If it asks for V30, use V30 or higher.
- Do not mix families. A device that asks for Class 10 may not get the expected speed from a U1 card, and a U1 device may not get it from a V10 card, even though all three say 10 MB/s.
A speed class is a floor for steady writing, not the peak speed some packages print.
What size microSD card do I need?
Capacity also comes in tiers, set by the SD Association, and older devices may not read the larger types:
| Card type | Capacity | File system |
|---|---|---|
| SD | Up to 2GB | FAT12, FAT16 |
| SDHC | Over 2GB to 32GB | FAT32 |
| SDXC | Over 32GB to 2TB | exFAT |
| SDUC | Over 2TB to 128TB | exFAT |
Check which types your phone, camera, drone or game console lists before buying a 64GB or larger card, since those are SDXC. Then pick a size from what the device records and how often you move files off the card.
MicroSD cards on Wiki Shopping
Of the 72 microSD cards listed on Wiki Shopping on October 26, 2026, 68 fall into one of five capacities: 8 at 8GB, 14 at 16GB, 16 at 32GB, 15 at 64GB and 15 at 128GB. Browse them under cell phones and accessories. For computer drives, see our guide to laptop storage sizes.
How we count
Capacities are read from each card's store listing. Cards without a stated capacity, or in a size with too few listings for its own page, are left out of those counts. The counts change as listings are added or removed.