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This SD card speed class guide explains the three markings that matter — V30, V60, V90, and UHS-I versus UHS-II — and why the right SD card for your camera depends on the exact recording mode, not a headline speed number.
Memory card packaging is built to sell speed, but the numbers printed on a card are not interchangeable. A card labeled 300 MB/s read, V30, U3, and UHS-I is making four different claims about four different layers of performance. Once you separate Video Speed Class from UHS Speed Class from bus interface, most card-buying mistakes disappear.
This page breaks down the full SD card speed marking system: the legacy C-class, the UHS U-class, the video V-class, and the UHS-I / UHS-II / UHS-III bus layers. It also shows exactly what current Sony and Canon cameras require for specific recording modes, because the camera manual — not a resolution chart — is the real authority.
The material is aimed at hybrid shooters and video creators who need to avoid two expensive errors: buying a V90 card the camera cannot exploit, or buying a card too slow for an All-Intra mode the camera unlocks only under the right class.
Quick Reference: Speed Markings at a Glance
| Marking | Guaranteed minimum sequential write | What it tells you |
|---|---|---|
| C2 / C4 / C6 / C10 | 2 / 4 / 6 / 10 MB/s | Legacy SD Speed Class floors |
| U1 / U3 | 10 / 30 MB/s | UHS Speed Class floors, using a different access method |
| V6 / V10 / V30 / V60 / V90 | 6 / 10 / 30 / 60 / 90 MB/s | Video Speed Class floors for sustained recording |
| UHS-I / UHS-II / UHS-III | — | Maximum bus rate: 104 / 312 / 624 MB/s |
The most important sentence on this page: a Video Speed Class number is a minimum sustained write guarantee, not a maximum transfer speed. A V90 card does not promise 90 MB/s peak performance. It promises that, under standardized conditions, the card will never drop below 90 MB/s during sustained video recording.
How SD Card Speed Markings Actually Work
SD cards carry four separate marking families, each governed by the SD Association under its own protocol.
The legacy SD Speed Class is the oldest layer. It covers C2, C4, C6, and C10, with guaranteed minimum sequential writes of 2, 4, 6, and 10 MB/s respectively. These classes date from the standard-definition and early Full HD era but still appear on modern cards.
The UHS Speed Class arrived with the UHS bus. It marks U1 and U3, which correspond numerically to 10 MB/s and 30 MB/s minimum performance. Despite sharing a number, U3 and V30 are not the same certification: they use different access methods tied to different generations of NAND and host behavior.
The Video Speed Class is the current standard for video. It defines V6, V10, V30, V60, and V90, with minimum sequential write floors of 6, 10, 30, 60, and 90 MB/s. This is the marking that matters most for camera video work.
A modern card may carry all three: C10, U3, and V30. That means it guarantees 10 MB/s under the legacy protocol, 30 MB/s under the UHS protocol, and 30 MB/s sustained under the video protocol. The numerical overlap is convenient but should not be read as one standard. A card can satisfy V30 while satisfying only C10 under the older access method.
Video Speed Classes: V30, V60, V90
The three classes photographers actually ask about are V30, V60, and V90.
- V30 guarantees 30 MB/s sustained write. It is commonly found on UHS-I cards and handles moderate-bitrate 4K, Full HD, and ordinary RAW bursts.
- V60 guarantees 60 MB/s sustained write. It is standardized for the UHS-II/UHS-III product families and covers higher-bitrate 4K and many hybrid workloads.
- V90 guarantees 90 MB/s sustained write. It is the highest Video Speed Class tier, also standardized for UHS-II/UHS-III, and is required by the most demanding All-Intra and high-frame-rate modes.
The SD Association's broad application guidance maps C10/U1/V10 to HD and Full HD, U3/V30 to Full HD and lower-bitrate 4K, V60 to higher-bitrate 4K and entry 8K, and V90 to 8K. But that broad map is the source of the most persistent myth in memory card buying.
"4K = V30" is not a reliable rule. A 100 Mbps 4K mode translates to about 12.5 MB/s, comfortably inside V30. A 600 Mbps All-Intra 4K mode translates to about 75 MB/s, which V30 cannot sustain but V90 can. The same resolution spans three different card classes depending on codec, bit depth, frame rate, and compression method.
The conversion from video bitrate to byte rate is simple: divide megabits by 8. A 280 Mbps mode is 35 MB/s. A 600 Mbps mode is 75 MB/s. But bitrate alone does not determine the required card class. Sony's official requirements prove exactly why.
UHS-I vs UHS-II: Bus Speed Is Not Card Speed
UHS-I, UHS-II, and UHS-III describe the card and host bus, not the card's guaranteed write floor.
| Interface | SDA maximum bus rate | 2026 relevance |
|---|---|---|
| UHS-I | 104 MB/s | Dominant mainstream and budget SD/microSD interface |
| UHS-II | 156 MB/s full duplex / 312 MB/s half duplex | Main high-performance SD interface for current cameras |
| UHS-III | 312 or 624 MB/s full duplex | Still defined by SDA, but little mainstream camera/card presence |
| SD Express | Up to 3940 MB/s | Current next-generation SD path via PCIe/NVMe |
The SD Association explicitly warns that bus-interface speed is not card speed. Actual performance depends on the card, the host device, the operation, and the data layout.
A UHS-II card is backward-compatible with a UHS-I host, but it operates within the lower host's ceiling. Put a 300 MB/s UHS-II card in a UHS-I slot and the bus caps the interface at 104 MB/s. The card does not make the camera write faster than its own pipeline allows.
The practical benefit of UHS-II shows up in two places: buffer clearing during long RAW bursts and card-to-computer offload. Where the camera has a UHS-II slot and a write pipeline that can exploit it, UHS-II reduces buffer-clear time and accelerates transfers. Where the slot is UHS-I, the premium is largely wasted.
What Your Camera's Recording Mode Actually Requires
The most useful way to choose a card is to look at the camera manual's exact mode table, not a generic resolution chart. Sony's a6700 is the clearest example because the same camera family requires U3, V60, and V90 for different modes.
| Sony a6700 mode | Nominal bitrate | Byte rate | Official card requirement |
|---|---|---|---|
| XAVC S HD | 100 Mbps | 12.5 MB/s | U3 or higher |
| XAVC HS/S 4K | 280 Mbps | 35 MB/s | SDXC V60 or higher |
| XAVC S-I HD | 222 Mbps | 27.75 MB/s | SDXC V90 or higher |
| XAVC S-I 4K | 600 Mbps | 75 MB/s | SDXC V90 or higher |
That table contains the clearest proof that bitrate math is not enough. The 222 Mbps XAVC S-I HD mode is only 27.75 MB/s on paper, yet Sony requires V90. The 280 Mbps 4K mode is 35 MB/s and requires only V60. The exact recording implementation matters more than the bitrate division.
Canon's current cameras show the same pattern within a single resolution and frame rate. The EOS R6 Mark II can require U3 for 8-bit 4K 59.94/50 IPB footage, but V60 for the same mode in 10-bit Canon Log 3 or HDR PQ. The bit depth changes the requirement even when resolution and frame rate stay identical. The EOS R5 Mark II carries this further: some SD-recordable 4K/Full HD modes require V60 or V90 depending on codec, while 8K RAW modes require CFexpress and do not support SD at all. Sony's α1 requires SDXC V90 or CFexpress Type A VPG200 for its 520 Mbps XAVC HS 8K mode.
The practical takeaway is simple: the camera's official requirement is the authority. Find the exact mode you plan to use, then buy the class it specifies.
How to Choose the Right Speed Class Without Overspending
The fastest card is not always the right card. The goal is to match the card to the camera's real write ceiling.
- Stills-only shooters and moderate burst photographers rarely see a practical difference between V60 and V90. A good V30 or V60 UHS-II card handles ordinary RAW bursts, while V90 adds little unless long high-speed bursts are routine.
- Hybrid shooters who stay in moderate 4K should look at V60 UHS-II as the sweet spot. It covers most current 4K modes up to the highest All-Intra and S&Q settings.
- Video creators using All-Intra 4K, S&Q, or high-bitrate modes need V90 where the manual specifies it. On Sony bodies like the a6700, V90 unlocks the full set of SD-compatible modes.
- Photographers who value offload speed benefit more from UHS-II's read performance than from a higher Video Speed Class. A card rated for 300 MB/s read clears a card reader noticeably faster than a UHS-I card capped at 104 MB/s.
V90 is frequently overbought by photographers who never run the modes that require it. The fastest advertised card does not clear a camera buffer any faster than the camera's own write pipeline allows. Buy only as fast as the modes you actually record require; put the saved budget into a second card or a UHS-II reader.
SDHC vs SDXC and Other Compatibility Traps
A speed marking alone does not make a card compatible with a camera mode. Capacity standard matters too.
- SDHC covers capacities greater than 2GB through 32GB. SDXC covers capacities greater than 32GB through 2TB.
- Some camera modes explicitly require SDXC, not just a speed class. A 32GB V90 card is SDHC and can be rejected for a mode that specifies SDXC, even though the speed mark is correct. Sony a6700 users have encountered exactly this error with 32GB V90 cards.
- SDHC normally uses FAT32, while SDXC uses exFAT. Reformatting a 32GB card as exFAT does not convert it into an SDXC-compliant product. Follow the camera's stated SDXC requirement.
The same C/U/V speed-class framework applies to microSD. A microSD card with V30 is a real V30 card, but for a camera with a full-size SD slot the adapter adds another mechanical interface. Sony supports microSD via an appropriate adapter on the a6700, but most photographers prefer native SD in full-size slots where possible. For action cameras, drones, and phone setups, see vlogging setup essentials.
Counterfeit and misrepresented cards remain a recurring buyer complaint. A card that tests fast in a benchmark but fails under sustained write, or a relabeled used card sold as new, can corrupt footage. Buy from a traceable seller and test a new card with a full-capacity write before critical work.
Current V30, V60, and V90 SD Cards Compared
The table below compares seven current cards across the three speed classes and both bus interfaces.
| Product | Class / bus | Max read / write | Tier | Link |
|---|---|---|---|---|
| SanDisk Extreme PRO SDXC UHS-I 128GB | V30 / UHS-I | up to 200 / 90 MB/s | Budget | Check price |
| Kingston Canvas React Plus V60 128GB | V60 / UHS-II | up to 280 / 100 MB/s | Mid-range | Check price |
| Lexar Professional 2000x Gold 128GB | V90 / UHS-II | up to 300 / 260 MB/s | Premium | Check price |
| ProGrade Digital Iridium V90 128GB | V90 / UHS-II | up to 300 / 200 MB/s | Premium | Check price |
| Sony SF-G128T TOUGH 128GB | V90 / UHS-II | up to 300 / 299 MB/s | Premium | Check price |
| Delkin Devices POWER V90 128GB | V90 / UHS-II | up to 300 / 250 MB/s | Premium | Check price |
| SanDisk Extreme microSDXC 128GB | V30 / UHS-I | up to 190 / 90 MB/s | Budget | Check price |
SanDisk Extreme PRO SDXC UHS-I 128GB — V30 budget workhorse
Specs and features:
- UHS-I, SDXC, U3/C10/V30.
- Up to 200 MB/s read and 90 MB/s write; V30 floor of 30 MB/s.
- Water, shock, temperature, and X-ray resistant; limited lifetime warranty.
Pros:
- Fast UHS-I read for offload without paying for UHS-II.
- V30 floor covers lower-bitrate 4K and Full HD.
Cons:
- UHS-I bus ceiling limits card-to-computer transfer.
- Not enough for high-bitrate All-Intra or S&Q modes.
Verdict: the right V30 card for photographers who shoot stills and occasional moderate-bitrate video. Perfect for beginners and single-card hybrid users on a budget.
Kingston Canvas React Plus V60 128GB — V60 hybrid sweet spot
Specs and features:
- UHS-II, Class 10, U3, V60.
- Up to 280 MB/s read and 100 MB/s write; V60 floor of 60 MB/s.
- Backward-compatible with UHS-I hosts; lifetime warranty.
Pros:
- V60 covers most moderate 4K modes without the V90 premium.
- UHS-II read helps offload.
Cons:
- Higher capacities in the family have faster write ratings, so speed must be checked at exact capacity.
Verdict: a strong hybrid-shooter choice for current cameras that stay below the highest All-Intra and S&Q settings. Perfect for a6700 and similar UHS-II bodies used in V60 modes.
Lexar Professional 2000x Gold 128GB — V90 high-bitrate
Specs and features:
- UHS-II, U3, V90.
- Up to 300 MB/s read and 260 MB/s write; V90 floor of 90 MB/s.
- Temperature, shock, vibration, and X-ray resistant; limited lifetime warranty.
Pros:
- High maximum write clears buffers quickly on capable UHS-II cameras.
- V90 floor unlocks the highest SD-recordable modes.
Cons:
- Excessive for stills-only or low-bitrate work.
Verdict: a premium V90 card for burst-heavy UHS-II bodies and high-bitrate video. Perfect for video shooters who use All-Intra 4K or long high-speed RAW bursts.
ProGrade Digital Iridium V90 128GB — modern V90 with capacity-dependent write
Specs and features:
- UHS-II, SDXC, U3, Class 10, V90.
- Up to 300 MB/s read and 200 MB/s write on this 128GB version; V90 floor of 90 MB/s.
- Refresh Pro compatible; 3-year warranty.
Pros:
- Recent Iridium generation tested for high-data-rate DSLR, mirrorless, and cinema workflows.
- Refresh Pro support can help maintain card health.
Cons:
- The 128GB version writes at 200 MB/s, below higher capacities in the family.
Verdict: a current V90 option with a solid sustained floor and useful maintenance features. Perfect for high-bitrate video and burst RAW on UHS-II cameras.
Sony SF-G128T TOUGH 128GB — rugged V90 with near-symmetric read/write
Specs and features:
- UHS-II, Class 10, U3, V90.
- Up to 300 MB/s read and 299 MB/s write in UHS-II; V90 floor of 90 MB/s.
- One-piece molded, ribless/switchless TOUGH design with IP68 dust and water protection.
Pros:
- Near-symmetric read/write makes offload and buffer clearing fast.
- Rugged build for field use.
Cons:
- Premium tier; the V90 floor is the relevant guarantee, not the 299 MB/s maximum.
Verdict: a top-tier V90 card for photographers who want durability and high offload speed. Perfect for travel and outdoor video work in challenging conditions.
Delkin Devices POWER V90 128GB — lifetime-warranty high-bitrate
Specs and features:
- UHS-II, Class 10, U3, V90.
- Up to 300 MB/s read and 250 MB/s write; V90 floor of 90 MB/s.
- Shockproof, waterproof, and X-ray proof; lifetime warranty; protective case included.
Pros:
- Strong sustained floor for high-bitrate video and multi-file capture.
- Lifetime warranty and included case.
Cons:
- Premium tier; overkill for stills-only use.
Verdict: a dependable V90 alternative for burst-heavy shooters who value warranty and protection. Perfect for video creators who regularly hit All-Intra and high-frame-rate modes.
SanDisk Extreme microSDXC 128GB — V30 for action and drone
Specs and features:
- microSDXC, UHS-I, U3/V30/C10/A2.
- Up to 190 MB/s read and 90 MB/s write; V30 floor of 30 MB/s.
- Water, shock, temperature, and X-ray resistant.
Pros:
- Same C/U/V speed-class framework as full-size SD.
- A2 rating covers random app performance, separate from video class.
Cons:
- Requires an adapter in full-size SD slots, adding an extra contact interface.
Verdict: the right V30 microSD for action cameras, drones, and smartphones. Perfect for vloggers and action-camera users who need a compact card for moderate 4K.
Frequently Asked Questions
Q: What does V30 vs V60 vs V90 actually guarantee?
They guarantee minimum sustained sequential write speeds of 30, 60, and 90 MB/s under SD Association-defined conditions. They are not maximum transfer speeds. A V90 card promises the write speed will not drop below 90 MB/s during sustained video recording, not that it peaks at 90 MB/s.
Q: Is UHS-II always faster than UHS-I?
Only when the camera has a UHS-II slot and a write pipeline that can use it. In a UHS-I host, a UHS-II card operates within the 104 MB/s UHS-I bus ceiling. The practical benefit of UHS-II shows in buffer clearing and card-to-computer offload on capable cameras.
Q: Do I need V90 for 4K video?
Not automatically. Lower-bitrate 4K often runs on V30 or V60, while 600 Mbps All-Intra 4K requires V90 on Sony's a6700. The camera manual's mode table determines the class. Resolution alone does not.
Q: Why does my camera reject a V90 card?
The most common non-counterfeit cause is capacity format. A 32GB V90 card is SDHC; some modes explicitly require SDXC, which starts above 32GB. The V90 marking cannot override a camera's SDXC requirement.
Q: Can I use a microSD card in a full-size SD slot?
Yes, with an appropriate adapter, and many cameras support this. The speed classes are the same. The adapter adds an extra mechanical interface, so native full-size SD is generally preferred for critical work.
Q: Does read speed matter for photography?
Yes, mainly for offload and review workflow. A card advertised at 300 MB/s read transfers files faster than a UHS-I card capped at 104 MB/s, but read speed does not improve in-camera video recording or buffer clearing the way sustained write does.
Conclusion
The right SD card is the one your camera's official mode table specifies — not the one with the highest number on the front. V30, V60, and V90 are minimum sustained write guarantees; UHS-I, UHS-II, and UHS-III are bus ceilings; and the manufacturer's 300 MB/s peak is a maximum, not a promise. Treating those three layers as one number is what leads to both overspending and rejected cards.
Start by identifying the exact recording mode you use most. If the manual says SDXC V60, buy a V60 UHS-II card and stop there. If it says V90 for your All-Intra 4K, buy V90. Check capacity format, buy from a traceable seller, and test a new card before critical work.
For a full comparison of current camera memory cards, see the best SD and memory cards for cameras. If you are building a video or vlogging kit, use the essentials to match the right card to your recording setup.
