SDHC, SDXC, and SDUC are capacity formats, not speed ratings.
SDHC cards run 4 – 32GB on the FAT32 file system (which caps any single file at 4GB, so long video gets split into chunks).
SDXC cards run 64GB – 2TB on exFAT (no practical file-size limit).
SDUC is the next step, 2TB – 128TB. The spec exists for these, but they’re not yet on sale and I know of know cameras that support it.
And plain SD is the original 2GB-and-under format you’ll only meet in vintage digital cameras.
For any camera made in the last decade, buy SDXC, 64GB or larger.
Speed is a separate set of symbols (V30/V60/V90, UHS-I/II) covered in my speed class guide.
| Format | Spec Introduced | Storage Capacity Range | Filesystem |
|---|---|---|---|
| SD (Secure Digital) | 1999 | 128MB to 2GB | FAT12/FAT16 |
| SDHC (Secure Digital High Capacity) | 2006 | 4GB to 32GB | FAT32 |
| SDXC (Secure Digital eXtended Capacity) | 2009 | 64GB to 2TB | exFAT |
| SDUC (Secure Digital Ultra Capacity) | 2018 | Over 2TB up to 128TB | exFAT |
Which one should you buy?
SDXC. Every camera released in the last ten years or so reads SDXC, the 64GB-and-up capacities make the most sense it terms of value and convenience. They also use exFAT as their filesystem, which means they support single files much larger than 4GB — that’s a crucial issue if you’re shooting 4K or 8K video.
Only buy SDHC if a specific older device says it can’t read SDXC (some cameras from before about 2010, and some older printers, TVs, and car systems).
Don’t wait for SDUC — there’s nothing to buy yet, and nothing to put it in. It won’t work in your existing camera.
What is SDUC, and can you buy one yet?
SDUC (Secure Digital Ultra Capacity) is the SD Association’s specification, announced in 2018, for cards from just over 2TB up to 128TB, using exFAT like SDXC.
As of this writing, there are no SDUC cards on the consumer market and no cameras that accept them; manufacturers only recently reached the 2TB ceiling of SDXC.
When SDUC does arrive, it will need SDUC-capable hosts — an SDUC card won’t work in today’s SDXC slots. File it under “good to know,” not “shopping list.”
Full-size SD vs. microSD
Before diving into capacities, it helps to clarify the physical shapes. The SD Association designs and controls the specifications for both major form factors.
- Full-Size SD Cards: These measure roughly 1.25 by 1 inch (32mm x 24mm). This is the standard physical size used by the vast majority of modern mirrorless cameras and DSLRs.
- microSD Cards: A much smaller physical footprint (microSD format) utilized primarily in action cameras, drones, and smartphones.
When it comes to the technology standards below (like SDXC and SDHC), the rules apply equally to both full-size SD and microSD cards.
The evolution of SD card formats
SD (Secure Digital)
The original SD specification was launched in 1999 as a collaboration between Panasonic, SanDisk, and Toshiba. It was designed to improve upon older formats by being physically thicker (and therefore more rugged), featuring an asymmetrical design so you couldn’t insert it backward, and adding copy protection.
These original cards utilized the FAT12 or FAT16 file systems and maxed out at a meager 2GB of storage. You will rarely see these outside of antique digital cameras.
SDHC (Secure Digital High Capacity)
Introduced in 2006, SDHC memory cards were the game-changers that broke past the 2GB limit. They were designed to meet the growing demand for digital photography, providing between 4GB to 32GB of available space.
SDHC cards use the FAT32 file system. While FAT32 is incredibly widely compatible across almost all devices, it has a significant drawback: the maximum size of any individual file is capped at 4GB.
This is fine for basic photos, but if you are shooting high-resolution 4K video, you will eat up 4GB in just a few minutes. To compensate, older cameras will automatically break long video recordings into multiple 4GB chunks — a highly annoying process known as chaptering.
SDXC (Secure Digital eXtended Capacity)
To solve the chaptering problem and accommodate modern video, the SDXC format was launched in 2009. SDXC supports a massive storage capacity ranging from 64GB all the way up to 2TB.
The key innovation here is the shift to the exFAT file system. This modernized file system supports incredibly large individual files, meaning your camera can record a continuous, uninterrupted 4K or 8K video file until the card is completely full. For almost all modern mirrorless and video shooters, SDXC is the standard you should be buying.
SDUC (Secure Digital Ultra-Capacity)
Announced in 2018, the SDUC format represents the next massive leap forward. While they look identical to existing cards, SDUC breaks the 2TB ceiling, supporting capacities from 2TB all the way up to 128TB.
Like SDXC, they utilize the exFAT file system to ensure there are no practical limits on individual file sizes. While it has taken years for manufacturers to hit the 2TB SDXC limit, SDUC ensures the physical form factor will survive the transition into heavy 8K RAW video and beyond.
Camera compatibility rules: What works where?
The SD format was developed with the principle of backward compatibility, but it’s a one-way street. If you put a brand-new card format into a very old camera, it will throw an error. Here are the practical rules to remember:
- SDUC Cards: Require host cameras that specifically support SDUC. You cannot put a 4TB SDUC card into a current-generation SDXC camera and expect it to work.
- SDXC Cards: Require cameras that specifically support SDXC. Almost all cameras made in the last decade do. However, if you find a vintage digital camera from 2008, an SDXC card will not work.
- SDHC Cards: If your camera supports SDXC (which modern ones do), it is fully backward compatible with older SDHC and standard SD cards.
Common questions
Can I use an SDXC card in a device that only says SDHC?
Generally no. SDHC-only devices don’t understand exFAT, so a 64GB+ SDXC card either won’t be recognized or will demand a format. The reverse works: any SDXC device reads SDHC and SD cards.
microSDHC vs microSDXC — same rules?
Yes. The capacity formats apply identically to microSD: 32GB and under is microSDHC (FAT32), 64GB and up is microSDXC (exFAT). Phones, drones, and action cameras that take microSD almost all support microSDXC today.
Does SDHC vs SDXC affect speed?
No. Speed is governed by the separate speed class (V30/V60/V90) and bus (UHS-I/UHS-II) ratings, which appear on both SDHC and SDXC cards. A V90 SDHC card is faster than a V30 SDXC card; it just holds less.
More to explore on SD cards
Understanding the difference between SDHC and SDXC is only half the battle — for the full picture of sizes, formats, and ratings, start with my guide to SD card types. Once you know the capacity you need, you must choose a card fast enough to handle your camera’s bitrate.
To avoid dropping frames or dealing with sluggish photo buffers, you need to understand the card’s write speed. I highly recommend reading up on the current generation of Video Speed Classes (V30 vs V60 vs V90).
If you want to dive even deeper into the future of memory media, check out my guide on the emerging high-speed format of SD Express, or check out my own independent speed tests on the market’s fastest SD cards.
