What are the A1 & A2 Ratings on SD and microSD Cards?

You might have seen new A1 and A2 speed ratings on some of the newer SD and microSD cards. So what do they mean? And when should you take notice of it? Here’s my straightforward explanation.

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Filed Under: Glossary, Memory Cards

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You might have seen new A1 and A2 speed ratings on some of the new SD and microSD cards. So what are they referring to, and should you take any notice of them?

The short version is that if you’re choosing an SD memory card for something like a camera, you can safely ignore the A rating and focus instead on the speed ratings that start with V or U.

If you’re using the card in a smartphone, tablet, or gaming device, then the A rating is much more useful and relevant.

And in that case, an A2 rating is designed for higher performance than an A1 card.

Basically, the A speed rating measures the kind of short-burst and fragmented reading and writing that apps and gaming devices use. The older U or V ratings measure a different type of speed where large amounts of data are written sequentially in a data stream (as in video).

A1 vs A2 SD Card Ratings Explained

SD and microSD cards have had several different speed rating categories. You see them in those small symbols and numbers on the cards and their packaging.

First, there was the speed class, which went from Class 2 to Class 10.

Then there was the UHS Speed Class, where the cards fall into either U1 or U3.

More recently, there’s a newer system, the Video Speed Class, that uses categories like V30, V60, and V90.

All of those are categories where the card is rated to meet or exceed a minimum threshold for sustained sequential write speed. Basically, that means they can keep up with a certain amount of data being recorded to them constantly. The obvious case where that comes into play is when recording high-definition (and ultra-high-definition (UHD)) video. The higher the quality and bitrate that the camera wants to record at, the faster the card needs to be to keep up with the stream of data coming at it. That’s why using a card that’s too slow in a 4K or 5K camera like a GoPro causes lockups and recording to stop–the card simply can’t keep up. One thing worth noting is that the actual speed you see in practical use is also very much dependent on the device you’re using it in, such as a camera or smartphone or another mobile device. In practice, the slowest link in the chain will determine the maximum speeds you get. So just because you have a very fast memory card doesn’t necessarily mean that you’ll see faster performance in practice.

So far, recording media like video and photos and audio has been the primary market that SD and microSD cards have been aimed at. So the speed rating systems have reflected that emphasis on recording high-resolution video.

But more and more, memory cards are being used to extend the memory of devices that run apps. Devices like smartphones and mobile gaming consoles like the Nintendo Switch, for example. The apps that run on these devices interact with memory space differently. Rather than a stream of sequential data, they want to write a lot of small chunks of data wherever there’s space available. That’s known as random read/write (compared to sequential read/write that’s important for video).

As you can clearly see in the speed test results I’ve posted, a card that is fast for sequential reading and writing isn’t necessarily fast for random reading and writing. So just because a card might be able to record very high bitrate 4K or even 8K video doesn’t necessarily mean that it’s going to be a good fit for the different kinds of use that applications might need.

As a result, the SD Association has come out with a new rating system specifically to categorize suitability for SD and microSD cards in application-heavy uses. It’s known as the Application Performance Class Specification, and it’s written in the form of A1 or A2. The idea behind it is that if you’re using the SD or microSD card to run applications on your mobile device, you can have confidence that a given card will be suitable before you buy it and will hopefully reduce the frustration of users buying cards blind that simply aren’t well-suited to running apps.

So far, there are only two designated classes: A1 and A2. The SD Association will add more as they’re needed. The thresholds to meet these categories are:


To display the A1 symbol, a card must meet or exceed these thresholds:

  • Random Read: 1500 IOPS
  • Random Write: 500 IOPS
  • Sustained Sequential Write: 10 megabytes per second


For the A2 category, it should be able to do at least:

  • Random Read: 4000 IOPS
  • Random Write: 2000 IOPS
  • Sustained Sequential Write: 10 megabytes per second


The “IOPS” here stands for input-output access per second. It’s a different measure than we’re used to with memory cards, where the speed has typically been measured in megabits per second or megabytes per second in keeping with how video bitrate is measured and visual media recorded to the card. But the IOPS measure is more meaningful for measuring the kinds of operations that apps do.

You’ll also notice that the specification also includes a minimum requirement for sequential write. The 10MB/s threshold corresponds to a Class 10 video speed rating, which is too slow for many of today’s cameras that record 4K, 5K, or 8K video.

Is the Application Performance Class Specification Relevant to Digital Cameras?

Not really. At least, not yet. If mobile cameras end up evolving into more app-heavy devices, maybe it will be more relevant one day. But we’re not there yet.

When shooting and saving photos and videos, the type of speed that matters with digital cameras is the minimum sequential write speed, because a large, constant stream of data (eg. HD video, 4K video, or even 8K video) needs to be written to the memory card at high speed.

It’s also worth pointing out that the A rating is a parallel rating system to the V and U systems. What I mean by that is that it doesn’t replace them, and it’s entirely possible–even likely–to have a card that carries both the A1 rating and a V30 rating or an A2 as well as a V90 rating. They’re referring to two different things.

A1 vs A2 SD Card FAQs

Are A1 and A2 SD card ratings relevant to drones?

No, not really. The type of SD card speed that matters when shooting photos and video footage with drones is the minimum sequential write speed. That type of speed is rated with a different metric and uses ratings such as V30, V60, and V90.

Does A1 and A2 affect storage capacity?

No, the storage capacity of the card does not directly affect the A1 and A2 ratings. The SDXC spec was designed by the SD Association so that higher capacity cards would also support the same speeds.

That said, not all SD cards have the speed–some are faster than others. But that speed relates to the performance design of the card and its internal components, not directly to the storage capacity.

Are A1 and A2 SD card ratings relevant to action cameras?

No, not really. The type of SD card speed that matters when shooting photos and video footage with action cameras such as GoPros is the minimum sequential write speed. That type of speed is rated with a different metric and uses ratings such as V30, V60, and V90.

What do A1 and A2 stand for on microSD cards?

A1 and A2 are Application Performance Classes that indicate the minimum random read and write performance of an SD card. A1 cards have a minimum random read speed of 1500 IOPS and a write speed of 500 IOPS, while A2 cards have a minimum random read speed of 4000 IOPS and a write speed of 2000 IOPS.

Which is better, A1 or A2 SD cards?

A2 SD cards are faster than A1 cards, offering better random read and write performance. However, your choice depends on your device and usage requirements. For most everyday tasks, A1 cards may suffice, but if you need higher performance, such as for gaming or running apps, A2 cards are better.

But the important thing to bear in mind is that the A1 and A2 speeds refer only to random write speeds. That is relevant for things like gaming devices and smartphones, but it’s not relevant in most cases for cameras, drones, and action cameras. For those, the more important rating system is the V system (eg. V30, V60, or V90).

What is the difference between UHS-I and UHS-II SD cards?

UHS-I and UHS-II (Ultra High Speed) are bus interfaces that indicate the maximum data transfer speed of an SD card. UHS-I cards have a single row of pins and offer speeds up to 104 MB/s, while UHS-II cards have two rows of pins and can reach speeds up to 312 MB/s.

Is UHS-II faster than UHS-I?

Yes, UHS-II cards offer potentially higher data transfer speeds than UHS-I cards. However, to benefit from the increased speed, your device must also support UHS-II.

How do I know which SD card is best for my needs?

To choose the best SD card, consider your device’s compatibility and your usage requirements. For everyday tasks, a Class 10, U1, or A1 SD card may be sufficient. For high-resolution video recording or gaming, a U3 or A2 SD card would be more appropriate. Always check your device’s specifications to ensure compatibility with the chosen SD card.

How do I read the codes and symbols on an SD card?

SD cards have various codes and symbols to indicate their speed class, application performance class, and UHS bus interface. For example:

– A number inside a circle (e.g., 10) indicates the Speed Class.
– A number inside a U (e.g., U1 or U3) indicates the UHS Speed Class.
– A number following a V (e.g., V30, V60, V90) indicates a newer (and faster) UHS Speed Class rating.
– A number following an A (e.g., A1 or A2) indicates the Application Performance Class.
Roman numerals (I or II) represent the UHS Bus Interface, with I being UHS-I and II being UHS-II.
– To determine the performance and compatibility of an SD card, consider these symbols and consult your device’s specifications.

What is the difference between microSD A1 and A2?

The difference between microSD A1 and A2 lies in their minimum random read and write speeds. A1 cards have a minimum random read speed of 1500 IOPS and a write speed of 500 IOPS, while A2 cards have a minimum random read speed of 4000 IOPS and a write speed of 2000 IOPS. A2 cards offer better performance, especially for running apps and gaming.

Does it matter which SD card I get?

Yes, choosing the right SD card matters because it can affect the performance of your device and the tasks you perform. Consider your device’s compatibility and your usage requirements when selecting an SD card to ensure optimal performance.

Memory Card Tools

Here are a few other related tools I’ve put together that can be useful when working with memory cards and data rates.

Converting Mbps to MB/s & X Speed Rating to MB/s

Another related and common calculation that often needs to be done when working with memory cards is converting the convention for measuring video bitrate (Mbps, Mb/s, or megabits per second) to the convention for measuring the speed of memory cards (MBps, MB/s, or megabytes per second).

So I’ve put together a simple calculator for that separately. You can find it here:

Memory Card Size Calculators

If you’re trying to figure out what size memory card to buy, it can be useful to know how much video footage from the camera you can fit on a card. Here are a few tools that can be useful for that:

Working with Memory Cards

Here are some related posts for making sense of memory cards and working with them.

David Coleman / Photographer

David Coleman

I'm a professional freelance travel photographer based in Washington DC. Seven continents, up mountains, underwater, and a bunch of places in between. My images have appeared in numerous publications, and you can check out some of my travel photography here. More »