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SD, SDHC, SDXC, and SDUC describe capacity standards, while SD, miniSD, and microSD describe physical sizes. A card works only when its size, capacity family, file system, speed class, and bus interface are supported by the host device. Check the camera, phone, console, recorder, or computer manual before buying; a slot labeled merely “SD” is not a complete compatibility specification.
What the SD, SDHC, SDXC, and SDUC labels mean
The letters on an SD-family card primarily identify its capacity standard and associated file system. They do not tell you whether the card is full-size or micro-sized, how fast it records, or whether it will fit a particular device. The SD Association defines four capacity families:
| Family | Standards-defined capacity | Typical file system specified by the standard | Compatibility implication |
|---|---|---|---|
| SD | Up to 2GB | FAT12 or FAT16 | Accepted by SD, SDHC, SDXC, and SDUC hosts |
| SDHC | Over 2GB through 32GB | FAT32 | Requires an SDHC-, SDXC-, or SDUC-capable host |
| SDXC | Over 32GB through 2TB | exFAT | Requires an SDXC- or SDUC-capable host |
| SDUC | Over 2TB through 128TB | exFAT | Requires an SDUC-capable host |
These are standards ranges, not a promise that every capacity is sold or that a device supports every value in the range. The SD Association lists the limits in its capacity overview.
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Older hosts may understand FAT12, FAT16, or FAT32 but lack exFAT support. An SDXC card therefore can fail in a host designed only for SD or SDHC, even though the contacts look similar. Reformatting does not add the missing host capability or turn an unsupported capacity family into a supported one. The SD Association recommends its own formatter for SD, SDHC, and SDXC cards rather than a generic operating-system formatter, but formatting should be treated as maintenance after compatibility has been established, not as a compatibility fix.
#1 Best Overall
- 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.)
Which card families work in which hosts?
The SD Association’s compatibility guidance can be read in either direction. A host’s label indicates the highest family it is designed to accept, while a card’s family indicates the minimum host capability it needs.
| Host marked as supporting | Card families accepted |
|---|---|
| SD | SD only |
| SDHC | SD and SDHC |
| SDXC | SD, SDHC, and SDXC |
| SDUC | SD, SDHC, SDXC, and SDUC |
| Card family | Hosts that support it |
|---|---|
| SD | SD, SDHC, SDXC, or SDUC hosts |
| SDHC | SDHC, SDXC, or SDUC hosts |
| SDXC | SDXC or SDUC hosts |
| SDUC | SDUC hosts only |
Use the device’s printed logo, user manual, or manufacturer support page to confirm the ceiling. The SD Association summarizes this as Match the Logo to your device
and advises checking the manual or manufacturer information at its capacity-choice guidance. A host that accepts SDXC does not automatically accept SDUC, and a host that accepts a microSD-shaped card does not automatically accept every microSD capacity family.
SD, miniSD, and microSD: physical size is a separate choice
Full-size SD cards measure 32 × 24 × 2.1 mm. microSD cards measure 11 × 15 × 1.0 mm, according to the SD Association’s capacity overview. miniSD is another, less common physical form. The SD Association notes that miniSD and microSD differ from standard SD in form factor, dimensions, pin arrangement, and whether a write-protect switch is present; its FAQ explains these distinctions.
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Rank #2
- 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.
Can a microSD card go in an SD slot?
Usually, a passive microSD-to-SD adapter lets the smaller card sit in a full-size SD-shaped shell. The adapter changes the physical shape and routes contacts; it does not change the card’s capacity family, file system, speed class, or bus capabilities. A microSDXC card in an adapter is still an SDXC card and still needs an SDXC-capable host. If the camera supports only SDHC, the adapter cannot make that card compatible.
Adapters also vary in practical quality. Insert the microSD card fully, keep the adapter’s lock tab in the unlocked position, and follow the host manual. Some devices specify an approved adapter arrangement or do not support adapters for recording. A full-size SD card normally has a write-protect switch; microSD cards do not, so the adapter’s switch is what the host may detect. Guidance for camera use and bus matching is also provided in this camera support article.
Speed classes and bus interfaces are not the same thing
Card packaging often combines several performance markings. Read them as separate specifications:
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.)
- Speed Class, UHS Speed Class, and Video Speed Class identify minimum sequential access performance under defined test conditions. They are especially important when a camera or recorder must sustain a required write rate.
- SD Express Speed Class is the corresponding class system for SD Express operation.
- Bus interface labels such as UHS-I, UHS-II, UHS-III, and SD Express describe the electrical interface and its theoretical maximum transfer rate.
- Advertised read or write speed is a card-specific result and is not guaranteed merely because a bus logo appears on the label.
The SD Association states: All speed class types assures minimum sequential card access performance including multiple stream access (in SD Express Speed Classes) under defined conditions specified by the standard.
Use the exact class requested by the host. A symbol with a similar number from a different class system is not necessarily interchangeable for device recognition. The Speed Class guidance explains the distinction.
Bus-rate ceilings
| Interface | SD Association theoretical maximum | What the number means |
|---|---|---|
| UHS-I | Up to 104MB/s | Bus capability, not a guaranteed card transfer rate |
| UHS-II | Up to 312MB/s half-duplex or 156MB/s full-duplex | Depends on both the extra-row host contacts and the card |
| UHS-III | Up to 624MB/s | Requires compatible host and card hardware |
| SD Express | Up to 3940MB/s | Requires an SD Express host and card path |
These figures come from the SD Association’s bus-speed overview. Actual performance is limited by the slowest component, the device’s firmware, the workload, and thermal or power conditions. A faster card can operate in a slower compatible bus mode, but it will not deliver its higher interface rate in a host that lacks that interface.
When A1 or A2 matters
Application Performance Class markings address random as well as sequential performance for running applications or storing application data. They are relevant to phones, tablets, handheld computers, and other hosts that explicitly support application storage. The SD Association defines A1 and A2 under specification test conditions in its Application Performance Class guidance.
Rank #4
- Fast for better pictures and Full HD video. Full HD (1920x1080) video support may vary based upon host device, file attributes, and other factors
- Great choice for compact to mid-range point-and-shoot cameras
- From 32GB to 256GB(1) to store tons of pictures and even more Full HD video(2). (1)1GB=1,000,000,000 bytes Actual user storage less
- Exceptional video recording performance with UHS Speed Class 1 (U1)(5) and Class 10 rating for Full HD video (1080p)(2). (5)UHS Speed Class 1 (U1) designates a performance option to support real time video recording with UHS enabled host devices
- Quick transfer speeds up to 100MB/s. Up to 100MB/s[64GB-256GB; 90MB/s for 32GB] read speed; write speed lower Based on internal testing; performance may be lower depending on host device, usage conditions, and other factors 1MB=1,000,000 bytes
An A2 logo alone does not guarantee A2 behavior. The host must support A2 features and commands; otherwise the card may deliver only the performance available through the host’s lower capability. For ordinary camera photos, video, or file transfer, choose according to the host’s required speed class and bus rather than paying for an application mark you cannot use.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.CFexpress, CFast, XQD, and CompactFlash are different formats
CFexpress, CFast, XQD, and CompactFlash are not larger or faster versions of SD. They use their own physical dimensions, connector arrangements, protocols, and specifications. The CompactFlash Association card-types directory treats them as separate removable-media standards, and some have multiple versions.
A camera can provide more than one slot, but that is a host-specific design decision. A CFexpress card does not fit an SD slot, and an SD card does not become CFexpress through an adapter. When a professional camera lists several formats, verify the exact card type and version for the slot you intend to use; do not infer interchangeability from similar speed claims. The device manual remains authoritative.
Best Value
- Great choice for compact to mid-range point-and-shoot cameras
- Quick transfer speeds up to 140MB/s (Up to 140MB/s read speed engineered with proprietary technology to reach speeds beyond UHS-I 104MB/s, requires compatible devices capable of reaching such speeds. Based on internal testing; performance may be lower depending on host device, interface, usage conditions and other factors. 1MB=1,000,000 bytes.)
- Up to 128GB to store tons of pictures (1GB=1,000,000,000 bytes. Actual user storage less.)
- Exceptional video recording performance with UHS Speed Class 1 (U1) Class 10 rating for Full HD video (1080p) (UHS Speed Class 1 (U1) designates a performance option designed to support real time video recording with UHS enabled host devices. See consumers speed page on SanDisk site. Full HD (1920x1080) video support may vary based upon host device, file attributes, and other factors. Visit the SanDisk Video Knowledge Base for more information.)
- Compatible with SanDisk SD UHS-I card reader (sold separately)
How to choose a compatible card
- Identify the physical slot. Determine whether the host takes full-size SD, microSD, or another format. If using an adapter, confirm that the manual permits it.
- Find the host’s capacity logo or maximum. Look for SD, SDHC, SDXC, or SDUC wording in the manual or on the manufacturer’s support page. Treat a generic “SD card” reference as incomplete until clarified.
- Select a capacity inside that family. For example, an SDXC-capable host can accept SD, SDHC, and SDXC, but not necessarily SDUC.
- Match the required speed class. For video or burst photography, use the minimum Speed Class, UHS Speed Class, Video Speed Class, or SD Express Speed Class specified by the host.
- Match the bus interface. Check whether the host supports UHS-I, UHS-II, UHS-III, or SD Express. The card’s interface can be faster than the host, but the system will operate at the host’s limit.
- Check application support when relevant. Choose A1 or A2 only if the device runs applications from the card and documents support for that class.
- Plan capacity and budget together. Capacity, sustained performance, and interface capability are separate costs. A smaller card that meets the host’s requirements is safer than a larger unsupported family.
- Format in the device when instructed. Back up files first. Use the host’s format command or the SD Association formatter recommended for the card family; formatting erases existing data.
Common failure symptoms and fixes
The device says no card or asks to format
- Confirm that the card family is within the host’s stated range; an SDXC or SDUC card in an older SDHC-only host is a common mismatch.
- Remove and reseat the card or adapter, checking for contamination or bent contacts.
- Check the full-size adapter’s lock tab. A locked tab can make a camera report write protection, although it should not prevent basic detection in every host.
- Back up the card elsewhere and format it using the device or the SD Association’s recommended formatter. Do not assume a successful computer format proves host compatibility.
Recording stops or produces dropped frames
Verify the minimum recording speed class and the host’s bus requirement. A card can advertise a high peak read speed yet fail a sustained write workload. Use a card with the class explicitly requested by the camera or recorder, and ensure the host supports the card’s bus mode.
Transfers are slower than the package claim
Check whether the reader and computer support the same bus as the card. A UHS-II card in a UHS-I reader cannot use the UHS-II ceiling, and a USB reader may itself be the bottleneck. The bus figures are maxima; real transfer rates vary with files, controller behavior, and the host.
Apps run poorly from a card marked A2
Confirm that the phone or tablet supports A2 operation. Without an A2-capable host, the card cannot deliver the class’s specified application performance. Also check whether the operating system permits adopted or portable storage for that card.
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- Physical size matches the slot, or the manual explicitly permits the adapter.
- Capacity family is supported: SD, SDHC, SDXC, or SDUC.
- File-system requirements are compatible with the host.
- Minimum sustained speed class meets the recording or application workload.
- Card and host share a supported bus interface.
- Any A1/A2 requirement is supported by the host, not just printed on the card.
- The exact camera, phone, recorder, console, or computer manual has been checked before purchase.
Applying all seven checks prevents the most common mistake: choosing by connector shape or advertised maximum speed alone.
Quick Recap
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