Best microSD cards in 2021: memory for phones, cameras, drones & more

Looking for the best microSD card for your smartphone, drone, security camera, dashcam or other recording device? We'll help you navigate you through the choices and jargon – and steer you to the best microSD card for you, at the best price.

The SD Card has been with us for a long time, spawning “mini” and “micro” sub-formats and a frankly mindboggling set of specification versions and speed classifications since its 1999 launch. All that means picking the best quality, and most cost-efficient, card for your device, can be a complete nightmare. It’s also important, since the market is a tempting one to counterfeiters.

Thankfully 20 years has seen the elimination of the ‘MiniSD’ format, reducing confusion somewhat; MicroSD has become the card of choice for action cameras, drones, security cameras and more besides. It has also become the de facto way to expand the capacity of (non-Apple) smartphones; look for the additional A1 or A2 “Application” ratings which provide a handy guide as to how useful the card will be if you’re storing apps and games on it (see the glossary below for more detail). The A2 performance class features command queuing and a cache, and can be written to about 4 times faster than A1 cards.

It's also worth familiarizing yourself with the size categories (again, see the glossary). There are several, but the most common now are SDHC (High Capacity), used by older devices, and SDXC, for cards over 32GB. 

Since a crucial factor is the speed of the data bus, older speeds are C2, C4, C6 and C10. These were superseded by UHS speed classes (C10 is around U1). The U classes refer to speed, but actually having UHS connectors (the roman numerals short for UHS-I or UHS-III) is another matter; UHS-II and above requires an extra row of connectors and only some devices are compatible with them.

Finally, if things weren’t confusing enough, there is also a Video Class Speed. These are about being able to record sustained streams without dropping frames. V30 will record 30MB/s, just like UHS-3, but more reliably for those recording video.

Best microSD cards in 2021

Hitting the A2 criteria is great news for phone users, and a V30 rating means there is also the write speed to shoot 4K on a modern device, so finally there might be a way to replace all that internal memory. There are lots of capacity options - here we quote live prices for the 256GB version, which is ideal for giving you lots of extra storage. 

Up to 20,000 hours of video recording as well as shock and ISO7816-1 x-ray protection, and IPX7 water protection, this is not only built for the endless over-write cycles of a security cameras & dashcams, but is also A1 certified.

The successor to Samsung’s dependable Plus series of cards, the Evo Select still hits all the right notes, while adding a 512GB option to the range. A reasonable price of getting high storage for phones, tablets and the Nintendo Switch as well as 4K video. Despite the missing ‘A’ certification it’s a quick card!

A lovely styling for true Nintendo lovers and a lifetime (or 30 year) warranty make this a great choice for game storage, in sizes from 64GB, though if you buy AAA titles online go straight for the 256GB.

Available in a good range of sizes, but at its most cost-efficient at 128GB and above, this is a good quality card with read speeds of 100MB/sec and write speeds not too far behind. Since it isn’t too expensive, it’s worth ensuring you’re getting the U3 version.

For the 8K future and the 4K now, this is one of the few cards available which meets the V90 specification. Kingston are confident of its reliability, even in temperatures from -25 to 85˚C,  that it comes with a lifetime warranty. On the subject of extras, atop the usual SD adapter is a USB adapter too, though it’s type A which doesn’t feel quite as futuristic as the card itself! (Usefully, on the subject of the past, the card is also backward compatible with UHS-I modes).

Kingston Endurance impresses with 20,000 hours of usage, but Samsung promise 43,800 (5 years, in other words) of full HD recording! Moreover it backs that up with a warranty (albeit with some smallprint). Samsung also claim it’ll survive 70 hours in seawater (though let’s hope there isn’t any of that in your helmet-cam).

Pioneer might be a brand you associate with your dad’s hi-fi separates, but that’s a pretty good thing when it comes to removable media; that 5 year guarantee is probably worth something, for a start.

V60 is the kind of speed that you’ll need to shoot 4K (depending on the bit rate) and 3D video with ever-more-capable devices, so it seems sensible to invest in UHS-II cards. This, though, is also backwards compatible (at slower speeds), so should your drone or action camera at up to 8K recording (not a claim the manufacturers make).

Some people don’t recommend putting this many digital eggs in such a small (and pricey) basket, but if keeping your smartphone photos and videos in the cloud fills you with fear, this is a MicroSD card available in sizes which compete with portable hard drives and boasts A2 capacity so you can run apps straight from the card.

The HC in SDHC stands for High Capacity, and the choice of those words is what left the industry needing XC soon after. If you’re trying to help out an older device limited to HC and U1, then the SanDisk Ultra is a good choice – as these may well warn you not to use larger than 32GB cards, due to incompatibility with more the more recent card format. (Note that the Ultra card is available in larger sizes - but with the SDXC logo which will mean it will be incompatible with these older devices).

MicroSD Glossary

A1 

Class 1 (A1) Application Performance Class also called SD Physical 5.1 spec, with a write speed of 10Mbytes/sec and minimum random read of 1500 IOPS (Input/Output Operations Per Second) and random write of 500 IOPS. IOPS is used because it’s a useful way of measuring the speed of the kind of computing operations that applications undertake, as opposed to simply reading or writing a large file.

A2 

Class 2 (A2) Application Performance Class also called SD Physical 6.0 spec, with a write speed of 10Mbytes/sec and minimum random read of 4000 IOPS (Input/Output Operations Per Second) and random write of 2000 IOPS.

FAT32 / exFAT

These are file systems – the FAT stands for File Allocation Table – and exFAT is the newer format for saving files (that’s not to say you aren’t old enough to remember FAT16, but it’s no use on newer SD cards). Since SDXC and their MicroSD equivalent cards came along, they’ve required use of the newer exFAT system, so it’s a good idea to be sure you use it too if you’re reading cards on computers.

Fragmentation

When a microSD card (or any disk system) stores a file, it might need to split it into pieces to fit around information already on the card. Over time adding and removing files can leave a number of fragments of files which will slow down accessing the card because the device needs to move between each fragment as it reads or writes. Thoroughly deleting the device (formatting and starting again) or using a defragmentation tool is a good solution

Megabits v MegaBytes

A byte is 8 bits, and a bit is the smallest unit of information storage on a microSD card. That means a data transferred at 10 Megabits per second would take eight times as long as 10 MegaBytes per second. 

Read/Write Speed

It’s usually quicker to read information off a card than to put it on, so look carefully at the quoted speeds. You’ll see a 

SDHC

Secure Digital High Capacity, otherwise known as Secure Digital version 2, arrived in 2006. This was the first step up in card size, from 2 to 32GB max, but used the same pins.

SDXC

Secure Digital eXtended Capacity. Announced in 2009 this was version 3 of the SD specification, adopting exFAT  file system and extending the theoretical storage limit to 2TB. 

SDUC

The next generation specification, settled in June 2018, supports cards up to 128 TiB (1 Tebibyte is 1024 GB), however it is still not in regular use yet. 

UHS

Ultra High Speed: This is the speed of the bus which transfers data to the host device. In the original SD Card is was 12.5 MB/S but this has increased with UHS-I, UHS-II and UHS-III. From UHS-II and onward MicroSD cards have 16 pins – an extra row – to achieve the new speeds.

Video Speed Class

Defines a set of minimum requirements for memory cards for recording progressive-scan video. They use a ‘V’ symbol followed by the same MB/s number seen in the original Speed Class. In other words, C6 and V6 are the same speed but only V6 will definitely record 1080P video.

Speed Table

With three different speed classes (plus A1 and A2), things can get a bit confusing. This table clarifies the speed equivalencies of the different speed classes, and what video you can record with it. It’s worth noting that, if you’re shooting video, you should get the fastest card you can rather than be guided by the ‘Max Video Resolution’ – for example a V6 card might be able to store 4K on some devices but a DJI FPV drone, which shoots good quality 4K video at 60fps, will consider anything below a V30 card “Too Slow”. 

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