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On an SD memory card, UHS means Ultra High Speed, but it can refer to two different labels: the card’s UHS-I, UHS-II, or UHS-III bus interface, and its U1 or U3 UHS Speed Class. The interface describes how the card communicates with a compatible device; U1 and U3 indicate minimum write speeds of 10 MB/s and 30 MB/s. Neither label alone guarantees a particular real-world transfer rate or video capability.
What does UHS mean on an SD card?
UHS is short for Ultra High Speed. The SD Association uses it for a family of SD bus interfaces: UHS-I, UHS-II, and UHS-III. These Roman-numeral labels describe the interface generation, not a card’s minimum write-speed class. The SD Association’s bus-speed overview lists the interfaces and their modes.
A card may also carry a UHS Speed Class symbol, U1 or U3. That is a separate performance mark: U1 specifies a minimum write speed of 10 MB/s, while U3 specifies 30 MB/s. The marks can apply to UHS-I, UHS-II, and UHS-III product families, so a U3 card is not necessarily UHS-III.
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The generations differ in their bus-interface modes and maximum interface rates. The values below are bus-speed figures listed by the SD Association, not guaranteed speeds for an individual retail card.
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- SPEED BARRIERS SHATTERED. Save precious moments with blazing read speeds up to 250MB/s(2) and write speeds up to 170MB/s(2) [256GB-1TB capacities(1)].
- MAXIMIZE WITH MASSIVE CAPACITY. Capture for longer and store more with up to 2TB(1) of storage that can hold up to 2,808 minutes of 4K UHD video recorded at 30 fps (641MB/minute)(9).
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| Interface | Listed bus modes and rates | What the figure means |
|---|---|---|
| UHS-I | 50 MB/s for SDR50 or DDR50; 104 MB/s for SDR104 | Mode-specific maximum bus rates |
| UHS-II | 156 MB/s full duplex; 312 MB/s half duplex | Rates for the listed transfer modes |
| UHS-III | 312 MB/s full duplex; 624 MB/s full duplex | Rates for the two modes shown in the Association’s overview |
These are interface ceilings, not a promise that a card will read or write at that rate. The Association cautions: “Maximum speed differs from the bus I/F speed. It varies depending upon the card performance.” Actual results also depend on the host device and the operation being performed.
What do U1 and U3 mean?
U1 and U3 are UHS Speed Class marks for minimum write performance, not bus generations.
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- CAPTURE LARGER THAN LIFE. Unlock 4K UHD(3) brilliance and pristine high res stills with video speed class ratings of U3 and V30(4).
- SPEED BARRIERS SHATTERED. Save precious moments with blazing read speeds up to 250MB/s(2) and write speeds up to 170MB/s(2) [256GB-1TB capacities(1)].
- MAXIMIZE WITH MASSIVE CAPACITY. Capture for longer and store more with up to 2TB(1) of storage that can hold up to 2,808 minutes of 4K UHD video recorded at 30 fps (641MB/minute)(9).
- DEFY THE ELEMENTS. Unrelentingly resilient, Sandisk SD memory cards are engineered to perform in extreme conditions, despite rough handling and constant use.(6)
- CONTENT MANAGEMENT, SIMPLIFIED. Back up, organize, and transfer everything easily with the Sandisk Memory Zone desktop app,(7) whether you use an SD card slot or a card reader.
| Mark | Minimum write speed | Use in interpreting a card |
|---|---|---|
| U1 | 10 MB/s | Indicates the class’s minimum write-speed requirement. |
| U3 | 30 MB/s | Indicates a higher class minimum write-speed requirement. |
For video, speed-class marks describe minimum sequential access performance under defined conditions. They are useful when checking recording requirements, but do not by themselves guarantee a particular resolution, frame rate, or recording duration. The SD Association’s video speed-class guidance lists V30 among the marks available in UHS-I mode, and V30, V60, and V90 among options for UHS-II and UHS-III modes. Check the camera’s required recording class and conditions in its manual.
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Choose by matching the card to the device and workload, rather than buying by Roman numeral alone.
Rank #3
- Save time with card offload speeds of up to 200MB/s powered by SanDisk QuickFlow Technology (Up to 200MB/s read speeds, engineered with proprietary technology to reach speeds beyond UHS-I 104MB/s, require compatible devices capable of reaching such speeds. Based on internal testing; performance may be lower depending upon host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes. X = 150KB/sec. SanDisk QuickFlow Technology is only available for 64GB, 128GB, 256GB, 512GB and 1TB capacities. 1GB=1,000,000,000 bytes. 1TB=1,000,000,000,000 bytes. Actual user storage less.)
- Pair with the SanDisk Professional PRO-READER SD and microSD to achieve maximum speeds (sold separately)
- Shot speeds up to 90MB/s (Write speed up to 90MB/s. Based on internal testing; performance may be lower depending upon host device. 1MB=1,000,000 bytes. X = 150KB/sec.)
- Perfect for shooting 4K UHD video and sequential burst mode photography (Full HD (1920x1080) and 4K UHD (3840 x 2160) video support may vary based upon host device, file attributes and other factors. See HD page on SanDisk site.)
- UHS Speed Class 3 (U3) and Video Speed Class 30 (V30) (UHS Speed Class 3 designates a performance option designed to support 4K UHD video recording with enabled UHS host devices. UHS Video Speed Class 30 (V30), sustained video capture rate of 30MB/s, designates a performance option designed to support real-time video recording with UHS enabled host devices. See the SD Association’s official website.)
- Check the device manual. Confirm which UHS interface the host supports and which card formats, capacities, and recording speed classes it accepts.
- Match the interface. The SD Association says a host performs best when paired with a card that supports at least the host’s interface. A faster-interface card does not make an incompatible host operate at that interface’s maximum.
- Match the workload. For sustained video recording, use the speed-class requirement specified by the camera for the intended recording mode. For other transfers, remember that card, device, and operation affect actual performance.
- Check capacity and format separately. SDHC, SDXC, and SDUC are capacity standards, distinct from UHS interface generations and U1/U3 speed marks. Verify that the device supports the card’s format and capacity.
These checks address separate compatibility questions: the bus interface governs communication with the host, the speed-class mark specifies a minimum performance tier, and format/capacity determines whether the device can use the card as intended.
Quick Recap
Best Value
- CAPTURE LARGER THAN LIFE. Unlock 4K UHD(3) brilliance and pristine high res stills with video speed class ratings of U3 and V30(4).
- SPEED BARRIERS SHATTERED. Save precious moments with blazing read speeds up to 250MB/s(2) and write speeds up to 170MB/s(2) [256GB-1TB capacities(1)].
- MAXIMIZE WITH MASSIVE CAPACITY. Capture for longer and store more with up to 2TB(1) of storage that can hold up to 2,808 minutes of 4K UHD video recorded at 30 fps (641MB/minute)(9).
- DEFY THE ELEMENTS. Unrelentingly resilient, Sandisk SD memory cards are engineered to perform in extreme conditions, despite rough handling and constant use.(6)
- CONTENT MANAGEMENT, SIMPLIFIED. Back up, organize, and transfer everything easily with the Sandisk Memory Zone desktop app,(7) whether you use an SD card slot or a card reader.
Rank #4
- Save time with card offload speeds of up to 200MB/s powered by SanDisk QuickFlow Technology (Up to 200MB/s read speeds, engineered with proprietary technology to reach speeds beyond UHS-I 104MB/s, require compatible devices capable of reaching such speeds. Based on internal testing; performance may be lower depending upon host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes. X = 150KB/sec. SanDisk QuickFlow Technology is only available for 64GB, 128GB, 256GB, 512GB and 1TB capacities. 1GB=1,000,000,000 bytes. 1TB=1,000,000,000,000 bytes. Actual user storage less.)
- Pair with the SanDisk Professional PRO-READER SD and microSD to achieve maximum speeds (sold separately)
- Shot speeds up to 140MB/s (Write speed up to 140MB/s. Based on internal testing; performance may be lower depending upon host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes. X = 150KB/sec.)
- Perfect for shooting 4K UHD video and sequential burst mode photography (Full HD (1920x1080) and 4K UHD (3840 x 2160) video support may vary based upon host device, file attributes and other factors. See HD page on SanDisk site.)
- UHS Speed Class 3 (U3) and Video Speed Class 30 (V30) (UHS Speed Class 3 designates a performance option designed to support 4K UHD video recording with enabled UHS host devices. UHS Video Speed Class 30 (V30), sustained video capture rate of 30MB/s, designates a performance option designed to support real-time video recording with UHS enabled host devices. See the SD Association’s official website.)
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