Whether you need it for a phone, a camera, or some other gadget, shopping for a microSD card may seem like a pretty simple thing to do. There's a lot more to them than you might realize, however. It's surprisingly easy to fall into several traps: overpaying, experiencing terrible performance, or the card not working in your device at all.

Are all microSD cards the same? Far from the case. Read on to learn all that you'll need to know.

1. Buying Incompatible SD Cards: microSD vs. microSDXC vs. microSDHC vs. microSDUC

All microSD card types are the same size and fit into all microSD card slots but are all SD cards the same?

The three main formats are SD, SDHC, and SDXC (or microSD, microSDHC, and microSDXC, as the micro and full-size cards are based on the same specs). The fourth format is SDUC.

Each format is defined in the SD specification, but they don't all work in the same way. As a result, these formats are not backwards-compatible. You cannot use newer microSD cards in hardware that only supports older formats.

sd card logos

The differences between microSD card formats are significant:

  • microSD has a capacity of up to 2GB and works in any microSD slot.
  • microSDHC has a capacity of more than 2GB and up to 32GB and works in hardware that supports either SDHC or SDXC.
  • microSDXC has a capacity of more than 32GB and up to 2TB and is only supported in SDXC-compatible devices.
  • microSDUC supports cards up to 128TB and will require a compatible device.

In addition to checking that a card's format is compatible with your hardware, you need to check a few other details, too.

Capacity

First, hardware supporting microSDXC slots doesn't automatically support all the other types of microSD cards available.

The Samsung Galaxy S20, for example, officially supports microSD cards up to 1TB and there's no guarantee that a higher capacity card will work, even though it may be based on the same spec.

kingston microsd card
Image Credit: Kingston

If you're planning to use your microSD card with a Mac at any point—for example, to move files on and off—you also need to ensure your computer supports the file system the card is formatted with. microSDXC cards use the exFAT system by default. Windows has supported it for years but macOS only since version 10.6.5.

Ultra-High Speed

The difference between microSD and SDXC (and SDHC cards, too!) lies in the card's ability to transfer data quickly.

The SDHC and SDXC formats can support the Ultra High Speed (UHS) bus interface—faster circuitry that enables data to move at a quicker rate. The three versions of UHS are UHS-I (with bus speeds of up to 104MBps), UHS-II (up to 312MBps), and UHS-III (up to 624MBps).

If you're looking to buy the fastest microSD cards to benefit from the increased performance of UHS, your hardware needs to support it. For example, UHS memory cards will work in older slots but with a reduced bus speed of 25MBps.

2. MicroSD Card Differences: Choosing the Wrong Speed

sd card specs

Identifying the difference between microSD cards in terms of speed is even more complicated. There are no less than six ways to show how fast a card is, and it's not uncommon for manufacturers to use all of them.

microSD Card Speed Class

microsd speed class

The Speed Class shows the minimum write speed of a memory card in megabytes per second. There are four Speed Classes to choose from:

  • Class 2: at least 2MBps
  • Class 4: at least 4MBps
  • Class 6: at least 6MBps
  • Class 10: at least 10MBps

Showing the base-level performance differences in microSD cards helps the manufacturer communicate whether a card is suitable for your needs.

Because this attribute tells you nothing about the SD card's maximum possible speed, it's technically possible for a Class 2 card to be faster than a Class 6 card. Class 10 cards should always be noticeably faster, though, as they have a bus speed of 25MBps (compared to 12.5MBps on Class 2 to Class 6 cards). Of course, the devil is in the details.

UHS Speed Class

uhs speed class icons

The UHS Speed Class shows the minimum write speed for microSD cards that support the UHS-I, II, and III bus speeds. We're listing it as a separate category because some manufacturers list both classes on their cards. The two UHS Speed classes are:

  • U1: a write speed of at least 10MBps
  • U3: a write speed of at least 30MBps

Application Performance Class

application speed class

The Application Performance Class specifies a minimum sustained write speed of 10MBps, along with a minimum random read and write speeds measured in input and output operations per second (IOPS). This guarantees an acceptable level of performance when storing and running Android apps on your card.

There are two classes:

  • A1: minimum random read speed of 1500IOPS; random write speed of 500IOPS
  • A2: minimum random read speed of 4000IOPS; random write speed of 200IOPS

The Application Performance Class is something you can look at when you're planning on installing Android apps on different types of microSD cards. It isn't a necessity, though, as SD cards without the A-rating may still perform adequately.

Video Speed Class

The Video Speed Class sets a minimum sequential write speed, which is essential when shooting video. The higher the resolution of your video, the faster the speed you need. There are five classes for video:

  • V6: minimum write speed of 6MBps
  • V10: minimum write speed of 10MBps
  • V30: minimum write speed of 30MBps
  • V60: minimum write speed of 60MBps
  • V90: minimum write speed of 90MBps

Rated Speed

While it's generally safe to assume that a higher Speed Class correlates to faster all-around performance, and UHS cards faster still, some manufacturers also quote a maximum speed for their products.

These speeds are in megabytes per second and help you pick out the absolute fastest microSD cards. However, the speeds are based on manufacturer tests, so they may represent a best-case scenario rather than real-world performance.

In practice, other external factors will affect read and write speeds. If you're copying files to your PC, for instance, your PC's specs—and even the USB cable you're using—will play a role.

Relative Speed

The other way manufacturers show the speed of their microSD cards is a throwback to the old CD writing days.

The original transfer rate for CDs was 150KBps. As our technology has improved, microSD card manufacturers would progressively advertise their microSD cards as being 2x, 4x, 16x faster, and so on, showcasing how many times faster than their predecessors they were.

You'll sometimes still see microSD cards labeled accordingly, although its relevance is declining. When a card is described as 100x, it means 100 x 150KBps, which is 15MBps. That finding was, again, likely produced under ideal lab conditions.

3. Picking the Wrong SD Card for the Task

When you buy a microSD card, it's important to pick one right for its intended use. This means finding a card that is large enough and fast enough, but not necessarily the largest microSD card out there. High-capacity UHS-II U3 cards often still have a price premium, and you won't always notice the benefits they offer.

If you're using a microSD card to store apps on your smartphone, consider one with an Application Performance Class rating. If you want a card so you can shoot 4K video on your phone, go for size and speed as a priority.

recommended microsd speeds

The SD Card Association recommends UHS Speed Class 3 (U3) or higher for shooting 4K video, and V60 or V90 for 8K video. For full HD video, it suggests a Class 10 or a Class 6 microSD card under certain circumstances. If your card's write speed is too slow, it will drop frames and produce stuttering video.

sd card speeds for video

For photography, some users prefer to have several smaller microSD cards rather than use a single larger one. This minimizes their risk of losing all of their photos at once if the card becomes corrupted.

If you're shooting RAW, where files might be 50MB or more, you'll benefit from an SD card boasting U1 or U3 speeds (They require at least SDHC format, however—one more tally to mark in the microSD vs. microSDHC debate).

There is no difference between a full-sized SD card and a microSD card in a microSD card adapter. If your camera only has an SD slot, you can still use a microSD card in it.

4. Buying Fake microSD Cards

It sounds like an obvious thing to avoid, but sadly, it's easy to be scammed into buying fake memory cards.

If you find a good deal on branded memory cards from a non-reputable seller, there's a real risk it may be counterfeit. In fact, many years ago, a SanDisk engineer reportedly told a reader of the Online Photographer blog that as many as one-third of all SanDisk microSD cards were counterfeit. It's unlikely that this number has declined since.

The buying guides on eBay include a page on spotting counterfeits because of how common they are. Amazon Warehouse sellers have been accused of foul play, too. If you're buying from a source that you're unsure about, check the reviews first.

Counterfeit cards correctly report the capacity shown on the packaging but actually contain far less. You won't notice this until the card fills up unexpectedly quickly, but there are utilities you can use to check the correct capacity. For Windows, try H2testw; and for Mac and Linux, you can use F3. Both tools are free.

5. Cheaping Out on Brands

That cheap, unbranded card you saw online might have some appeal, but we'd advise that you steer clear of any microSD cards that come from manufacturers that you cannot verify. We've all owned microSD memory cards that have stopped working for no apparent reason. microSD cards do fail, and when they do, they'll take all your data with them.

For this reason, buying cards from big brands will always be better than buying no-name cards on the cheap. You can expect better performance, greater levels of reliability, and housing that protects your cards against shock, water, and even airport X-rays.

Name brands also offer things like a lifetime warranty and access to image recovery software. For Lexar microSD cards and SanDisk microSD cards, this is considered a standard.

Are All MicroSD Cards the Same?

It's far from the case that all memory cards are the same. The good news: everything that you need to know is right here for you.

Now, all that you need to do is figure out the right one for your needs. Speed? Capacity? The truth is out there. It's time for you to go out there and grab a slice.