SD Card Types Explained: Sizes, SDHC vs SDXC vs SDUC, Speed Classes and UHS

“SD card types” means three different things, and the label on any card has all three identified:

• Physical size: full-size SD (cameras) and microSD (phones, drones, action cameras; fits an SD slot with an adapter).³
• Capacity format: SD, SDHC, SDXC, and SDUC — the “four types” people usually mean, and they set the card’s capacity range and file system, not its speed.
• Speed and interface: the V30/V60/V90 (and older U3/Class 10) speed classes, the A1/A2 app ratings, and the UHS-I / UHS-II / SD Express bus that caps how fast data can move at all. Pick a size your device takes, SDXC for anything modern, and the speed rating your camera’s video mode needs — that’s the whole decision.

I spend a lot of time putting memory cards through their paces for my independent SD card speed tests and microSD card tests. I’ve used nearly every generation on the market, and I know from personal experience that not every type of SD card works well in every device. And sometimes, paying a premium for the latest and greatest SD card can actually cause bottlenecks in older hardware.

So here’s a rundown of the different kinds of codes and technology you’ll find in SD cards and what to look for to match your device.

SD card types at a glance

What varies	The options	What it controls	What to buy for a camera
Physical size	SD (full-size), microSD; miniSD (obsolete)	Whether it fits the slot. microSD works in SD slots via adapter	Whatever your camera takes; full-size SD for most cameras, microSD for action cams/drones
Capacity format	SD (≤2GB), SDHC (4–32GB, FAT32), SDXC (64GB–2TB, exFAT), SDUC (2–128TB, not yet on sale)	Capacity range and file system (FAT32 splits video at 4GB)	SDXC, 64GB or larger, for any camera from the last decade
Video speed class	V30, V60, V90 (older: U1/U3, Class 10)	Guaranteed minimum sustained write speed: 30/60/90 MB/s	V30 for most 4K; V60/V90 for high bitrates, long bursts, RAW video
App performance class	A1, A2	Random read/write for running apps	Irrelevant for cameras; A2 for Switch/Steam Deck
Bus interface	UHS-I (~104 MB/s), UHS-II (~312 MB/s), SD Express (PCIe, up to ~4,000 MB/s)	The speed ceiling; the slot must match to benefit	Match the slot: UHS-II only if the camera has a UHS-II slot; avoid SD Express in UHS-II cameras (see the trap below)

SD card types explained: SD, SDHC, SDXC, SDUC

While they are all commonly lumped together as “SD cards,” there are actually four sub-types of secure digital formats:

• SD (or SDSC)
• SDHC
• SDXC
• SDUC

These codes aren’t performance ratings. They’re classifications defined by the SD Association (the organization that controls the SD specs) that dictate the card’s filesystem and its maximum storage capacity.

What’s the difference between SDHC and SDXC?

SDHC (Secure Digital High Capacity) cards max out at 32GB and use the FAT32 filesystem. SDXC (Secure Digital eXtended Capacity) cards range from 64GB to 2TB and use exFAT. For modern video shooters, SDXC is highly preferred because it allows cameras to record long, continuous clips without splitting them into annoying 4GB chunks.

The most common formats you’ll find available today are SDHC and SDXC cards. And they’re the most relevant for cameras.

The original SD standard is obsolete. And right now, SDUC hasn’t hit the consumer market in any meaningful way, so you can safely ignore them.¹

The SD Association strictly ties capacity to filesystems.

Cards that are 32GB or smaller are formatted as FAT32 and fall within the SDHC category. Cards 64GB and larger are formatted with exFAT and are categorized as SDXC.

So, as a practical matter, if you buy a 32GB card, it will always be SDHC. If you buy a 128GB card, it will always be SDXC.²

Format	Capacity	File system	In practice
SD (SDSC)	up to 2GB	FAT12/FAT16	Obsolete; only for very old cameras
SDHC	4GB – 32GB	FAT32	Works everywhere, but FAT32 splits long video into 4GB chunks
SDXC	64GB – 2TB	exFAT	The standard for any modern camera; unbroken video files
SDUC	2TB – 128TB	exFAT	Specified, not yet on the shelves; needs SDUC-capable devices

Those four are what people mean by “the four types of SD cards.” The only one that matters when you shop is the SDHC/SDXC line: 32GB and under is SDHC, 64GB and up is SDXC, and for any camera that shoots video you want SDXC. If you want more detail, I go through the history, the compatibility rules, and the SDUC question in detail in SDHC vs SDXC vs SDUC.

Compatibility

The SD system is designed to be backward compatible.

What that means in practice is that if a camera supports SDXC, it will also read older SDHC and standard SD cards. And every current camera I can think of supports SDXC.

However, there are some older digital cameras that only support SDHC. And those will not be able to read a modern 128GB SDXC card, for example.

SD card speed classes: How to choose for photography & video

Buying a fast card has no impact on image quality and won’t make you a better photographer, but getting a card that is fast enough is critical if you want to use your camera’s features without risking glitches.

If your card can’t keep up with your camera’s data pipeline, the buffer will choke, video recordings will randomly stop, and the camera might completely lock up while it struggles to write files.

To help sort this out, the SD Association created several “Speed Classes” to indicate the minimum sustained write speed a card can guarantee.

There are two primary categories you need to care about. If you are shooting video or photos, you want to look at the Video Speed Class (marked with a V, like V30 or V90). If you are buying a card for a handheld gaming console or smartphone, you want to look at the Application Performance Class (marked with an A, like A1 or A2).

Understanding “Speed”

When manufacturers print big, bold speed numbers on the front of the card, they are almost always advertising the “Read Speed” (how fast data moves off the card to your computer). Read speeds are generally much faster than write speeds, which makes them great for marketing.

But for a camera, Write Speed (how fast data moves onto the card) is what actually matters. Specifically, cameras need high sequential write speeds to lay down a constant, unbroken stream of video data. Gaming devices, on the other hand, need high random read/write speeds to juggle thousands of tiny texture files and save states simultaneously.

Decoding the ratings

Megabytes vs. megabits

SD card speeds are measured in Megabytes per second (MB/s — capital B). Video recording bitrates in your camera menu are usually measured in Megabits per second (Mbps — lowercase b).

They are not the same thing. Because there are 8 bits in a byte, you have to divide the camera’s Mbps by 8 to figure out what MB/s card speed you actually need. For example, if your camera shoots 400 Mbps video, it only requires a sustained card speed of 50 MB/s. Here’s a handy conversion calculator.

The “x” Rating: Some brands, notably Lexar, still use an older “x” multiplier system based on the read speed of 1990s CD-ROM drives (where 1x = 150 KB/s). It’s an outdated metric, but if you need to translate it into modern MB/s, you can use this simple tool:

SD card Video Speed Classes

Symbol	Guaranteed minimum sustained write	Use it for
V30 (= U3)	30 MB/s	Most 4K from consumer cameras, drones, action cams
V60	60 MB/s	High-frame-rate or high-bitrate 4K; the hybrid-shooter sweet spot
V90	90 MB/s	8K, ALL-I and RAW-on-SD codecs, long RAW bursts
Class 10 / U1	10 MB/s	Legacy 1080p; ignore when a V rating is present

The number is the card’s guaranteed minimum sustained write speed in MB/s; divide your camera’s bitrate in Mbps by eight to see what you need. Every symbol, and which class your camera actually requires, is covered in my guide to SD card speed classes — and whether a faster card is worth it for your specific camera in what memory card speed your camera actually needs.

What is the a rating (A1 & A2)?

The Application Performance Class (A1 and A2) was created specifically for smartphones and gaming devices that run applications directly from the memory card.

It’s not relevant to cameras.

Running an app requires rapid, random read/write speeds, bouncing small packets of data around the memory architecture. If you are buying an SD card for a camera, you can entirely ignore the A-rating. But if you are expanding the storage on a Nintendo Switch or a Steam Deck, I highly recommend looking for an A2-rated card, which guarantees a much higher baseline of random IOPS performance for smoother gaming.

UHS-I vs. UHS-II vs. SD Express

The UHS (Ultra High-Speed) designation refers to the physical bus interface — essentially, the internal highway connecting the card to the device.

UHS-I vs. UHS-II: The Physical Difference

UHS-I cards have a single row of contact pins and max out at 104 MB/s.
UHS-II cards feature a second row of contact pins, allowing them to reach up to 312 MB/s. They are backward compatible, meaning you can put a UHS-II card in an older UHS-I camera, but it will simply drop back to slower UHS-I speeds.

In the field, taking advantage of UHS-II requires both the card and the camera slot to support it. Paying for a UHS-II card when your camera only has a UHS-I slot is a common trap that provides no in-camera performance bump (though it will offload to your computer faster if you have a UHS-II card reader).

Bus Speed Class	Maximum Bus Speed	Compatibility
Ultra-High Speed I (UHS-I)	50–⁠104 MB/s	SDHC / SDXC / SDUC
Ultra-High Speed II (UHS-II)	156–⁠312 MB/s	SDHC / SDXC / SDUC
Ultra-High Speed III (UHS-III)	312–⁠624 MB/s	Vaporware (Essentially abandoned)
SD Express	985–⁠3940 MB/s	SDHC / SDXC / SDUC

Additional SD card variants & modern pitfalls

SD Express & the backward compatibility trap

To compete with the blistering speeds of CFexpress cards (a competing standard), the SD Association introduced SD Express.

This technology integrates the PCIe and NVMe architectures found in modern computer SSDs directly into the SD form factor, theoretically allowing for transfer speeds approaching 4000 MB/s.

Adoption was painfully slow for years, but that changed recently when Nintendo adopted microSD Express for the Nintendo Switch 2, pushing the format into the mainstream.

However, you need to be extremely careful where you use these cards due to a major backward compatibility trap.

SD Express uses the second row of pins on the back of the card for its PCIe interface. These are the exact same pins that UHS-II cards use for their extra speed. Because the card cannot use those pins for two different protocols at once, most SD Express cards do not support UHS-II fallback.

If you put a bleeding-edge, hyper-expensive SD Express card into a high-end mirrorless camera that expects UHS-II (like a Sony a7RV or Nikon Z8), the card will drop all the way down to baseline UHS-I speeds. Overpaying for an SD Express card can actually make your camera perform worse than a standard V90 card.

SD vs. CFexpress Type A

CFexpress cards are an entirely different format managed by a competing group (the CompactFlash Association). There are three sizes: Type A, Type B, and Type C.

CFexpress Type A cards are slightly smaller and thicker than standard SD cards. They are not natively compatible. However, cameras like the Sony a1 and a7S III feature brilliant dual-format slots that can accept either an SD card or a CFexpress Type A card in the exact same slot. This is a proprietary design; you cannot force a CFexpress Type A card into a standard SD card reader.

Industrial-grade SD cards

You may see “high endurance” cards marketed for dashcams or security cameras that record continuously on a loop. Industrial-grade cards take this further with wider operating temperature ranges and hardened durability.

For the vast majority of photographers, there is no reason to seek out expensive industrial cards unless you are mounting a time-lapse rig in a freezing polar region or a blistering industrial setting.

Best types of SD cards for . . .

Use Case	Recommended SD Card Type	Key Features to Look For	Notes
Cameras	UHS-I or UHS-II cards with U3, V30, V60, or V90 speed ratings	Sequential write speed for continuous shooting, burst mode, and high-bitrate video.	Check your camera’s manual. Do not overpay for V90/UHS-II if your camera only has a UHS-I slot.
Gaming Devices	A1 or A2 rated SD cards	High random write speed to handle numerous small data transfers (for game saves and app data).	The original Nintendo Switch and Steam Deck benefit greatly from A2-rated cards.

Common questions

What are the 4 types of SD cards?

SD, SDHC, SDXC, and SDUC — the capacity formats. SD tops out at 2GB, SDHC at 32GB (FAT32), SDXC at 2TB (exFAT), and SDUC runs to 128TB but isn’t on sale yet. If you mean physical sizes, there are two that matter: full-size SD and microSD.

Are all SD cards the same size?

No. Full-size SD (32 × 24mm) is what most cameras use; microSD (15 × 11mm) is for phones, drones, and action cameras, and slides into a full-size slot with a passive adapter. miniSD existed briefly and is gone.

What’s the difference between SDHC and SDXC?

Capacity and file system. SDHC is 4 – 32GB on FAT32 (which caps any single file at 4GB, so video gets split); SDXC is 64GB – 2TB on exFAT (no practical file-size cap). Neither label says anything about speed. Details in SDHC vs SDXC vs SDUC.

Can I use an SDXC card in a camera that only lists SDHC?

Usually not — an SDHC-only device can’t read exFAT. Newer devices are backward compatible (SDXC slots read SDHC and SD), but it doesn’t work the other way.

Is microSD the same as SD?

Same standards, smaller card. microSDHC/microSDXC follow exactly the same capacity and speed rules as their full-size counterparts; they just tend to top out lower in real-world speed, which is why I test them separately (microSD speed tests).

Cameras

I always check the camera’s manual to confirm the slot limits. If you have a UHS-I slot, a V30 card is usually the most cost-effective solution. If you have a modern UHS-II slot and shoot 4K video, a V60 card is often the sweet spot for balancing performance and price.

Nintendo Switch (original / OLED) & Steam Deck

Look specifically for the A1 or A2 Application Performance Class rating. The original Switch hardware is limited to UHS-I speeds, so do not spend extra money on UHS-II cards; you will see zero benefit.

Nintendo Switch 2

The Switch 2 supports PCIe architecture. Look specifically for microSD Express cards. While the console is backward compatible with older cards, using an Express card will give you load times comparable to an internal SSD, which is crucial for modern games.

General SD card workflow advice

• The Golden Rule: My absolute golden rule for memory cards is to format them in the exact camera you plan to use them in. This ensures the file system and folder hierarchy are built to the camera’s exact specifications, drastically reducing the risk of file corruption in the field.
• Buy from Reputable Sources: Flash memory is incredibly easy to counterfeit. Buy from trusted, dedicated retailers (like B&H Photo) rather than third-party marketplace sellers.
• Backup Regularly: SD cards are consumable items, not archival media. Offload your files to an external drive or cloud service as soon as your shoot is over.

How to recover data from an SD card

If you accidentally format a card or delete an image in-camera, do not panic, and stop shooting immediately.

Most cameras perform a “high-level format” (or quick format), which simply wipes the directory index but leaves the actual image data untouched on the flash memory. As long as you don’t write new photos over that invisible data, you can usually pull the card out, plug it into your computer, and use desktop software to scan the drive.

I have a detailed, step-by-step guide on exactly how to recover deleted photos using software like Disk Drill if you find yourself in this situation.

Notes & References:

1. SanDisk announced a 4TB SDUC card at NAB 2024, but nearly two years later you still can’t buy one at retail. [↩︎]
2. Technically, you can force a computer to format a 32GB SDHC card with exFAT, but doing so violates the SD Association spec, can cause workflow errors in cameras, and will simply be overwritten the next time you format the card in-camera. If you need to wipe a card cleanly on a computer, I recommend using the official free SD Card Formatter application. [↩︎]
3. Another physical size, miniSD never took off and is long dead. [↩︎]