Android and SD cards: The Ultimate Guide

Android has supported SD cards since the G1 started it all. The overall idea is simple enough — slap an SD card in your phone and expand the storage so you have room for more stuff. While this is mostly the case, there are a few things to know about, especially before you go out and buy one.

We've rounded up everything you need to know about buying and using an SD card with your Android to try and make everything as simple as it can be.

SD card form factors

SD card sizes

Before you do anything, make sure your phone can use an SD card! Since so many different companies make Android phones in so many different models, you will run across some that don't have a slot for a card. Phones from Google are this way, and every name you recognize when it comes to making phones has made at least one model that doesn't have support for an SD card. If you're not sure, poke around the outside of your phone to see if any doors or flaps open up, or grab the manual out of the box and see what it says.

Phones use the smallest microSD card form factor.

Once you've got that sorted, you need to make sure you get the right type of SD card. For your Android phone, you're looking for the microSD form factor. SD cards come in three different sizes. An SD card is the biggest — a little larger than a postage stamp — and is used for things like standalone cameras. The Mini SD form factor is about half the size of a full SD card and they aren't very popular. Chances are you won't ever buy anything that needs a Mini SD card. The microSD card is about the size of your fingernail and the one we're looking for.

When you buy a microSD card, you often get an adapter in the package. The smaller card slides into the adapter so it can fit into something that needs a full-size card — like your computer — as well as something like your phone that needs a microSD card. Keep track of this, because it's pretty handy when transferring pictures or video from your phone to your computer.

SD card storage versions

SD cards

There is a method to the madness of all those letters you see.

The next thing you need to know is the storage version. You can buy microSD cards, microSDHC cards, and microSDXC cards. A microSD card was designed to hold up to 2GB of information, though a few 4GB versions are available that work outside of the specifications. microSDHC cards (Secure Digital High Capacity) are designed to hold up to 32GB of data. microSDXC (Secure Digital eXtra Capacity) cards are designed to hold between 32GB and 2TB of data. It's important to know what version your phone can use. Most modern phones — Android or otherwise — will be able to use a microSDHC card. Many newer phones are capable of using a microSDXC card.

There are no easy-to-see differences between a phone that can use a microSDXC card and one that can't. You'll need to consult the documentation that came with your phone or hop into the forums and ask other folks who have already found the answer. The versions are backward compatible (a microSDXC card slot can use a microSD or microSDHC card) but there is no forwards compatibility, and if your phone can't use a microSDXC card, it won't ever work.

SD card speed classes

MicroSD card

No card is going to be as fast as the listed maximum.

You need to understand the speed class ratings. Those are the numbers and letters you see printed on the card and the packaging. The short version is to never buy one with a number lower than 10 when it comes to speed class, and if you use a phone with a 4K camera, go even faster and look for a UHS class card.

We've broken down the specifics of what all this really means and which you need, and you can read that right here:

Everything you need to know about SD card speeds and your phone

Adoptable storage and you

You'll probably see people talking about adoptable storage when SD cards and Android are in the conversation. It's a really neat thing that your phone probably doesn't have and chances are you're better off for it.

The idea is to use a fast SD card and make it a permanent part of the system. Once it goes in, it never can come out or all your stuff stops working. It's also a part of the phone it came out of and nothing else will be able to use it unless you reformat it and start over.

This, and concerns about performance, is why most companies making Android phones don't let you use Adoptable storage without hacking it in yourself. On Android things that aren't phones — like the NVIDIA Shield TV for example — you can plug in USB stick drives or hard drives and "adopt" them into the system. This makes a little more sense and a 500GB USB drive is a great match for your Android TV box. We go into details at the link below.

Everything you need to know about your SD card and Adoptable storage

Should I encrypt my SD card?

This is one of those things that if you have to ask, the answer is usually no.

SD card encryption is a great way to make sure nobody can see anything you have stored on your card without being able to sign into your phone, but there are a few drawbacks:

  • It takes a little longer to read something from or write something to the SD card. Not a lot but it's a definite thing.
  • You can't take the card out and do something like transfer pictures and music from a computer.
  • If your phone dies, you've lost everything on the card because your phone is the only thing that can decrypt it.

Keep all this in mind if you decide to try it, and make sure to have a good plan to keep your data backed up somewhere else.

Quick Q&A

MicroSD card

  • How should I format my SD card? Insert it into your phone and follow the instructions in the notification you get. Since there are several different file formats an SD card can use, you should let the phone pick the one it wants. Don't worry, your card will still work in a computer to copy files.
  • Do SD cards go bad? Yes, but that's becoming less of a thing with recent cards. Your SD card has a limited amount of times it can be read from and written to before it starts to have errors. If you start to get errors when you are using it, consider buying a new one before it goes bad. As mentioned, newer cards last longer than cards from just a few years ago.
  • Is my SD card waterproof? Maybe. It will say on the packaging if it is designed to get wet. Always try to not let it get wet, but if it does, don't stick it into anything until it dries, then take a Q-tip and some 99% rubbing alcohol and clean the copper contacts on the end you plug in. Let that dry and give it a try.
  • Why does Google hate SD cards? I don't think it hates them because every Chromebook can use one. Officially, Google says SD cards are not as secure and having more than one storage drive is messy for the end user. Feel free to add your own theory here.
  • Which SD card should I buy? Only you know the answer based on how you will use it. We've done our research, and you can check out our favorites here:

Best microSD Card for Android

When it comes to using SD cards in your phone, things don't need to be confusing. After you see all the hype from companies making them, take a minute or two and read through this again, then think about what you need a card to do. It really is that simple.

Jerry Hildenbrand
Senior Editor — Google Ecosystem

Jerry is an amateur woodworker and struggling shade tree mechanic. There's nothing he can't take apart, but many things he can't reassemble. You'll find him writing and speaking his loud opinion on Android Central and occasionally on Twitter.

  • Bought a Lexar 16g HC1 card and after a year it just started sending error messages,then asked for a formatting of the card...just threw it away
  • I've come to conclude that Lexar cards are crap. A 128GB Lexar I had got corrupted (was unable to format or write), RMA'd it, got my replacement 2 months later. The replacement card studders with *music playback*. Bag of trash.
  • Actually the studder shouldn't be a "problem" due to something broken. Usually it's a result of slow write speeds. Happens more often for video. You just gotta buy a faster card. You get what you pay for.
    If a little part of the data is broken, simply, the whole thing wouldn't work at all.
  • What about the new Samsung UFS card speed of 530 megabytes per second? Any news?
  • UFS is a different form factor (shape) and won't be compatible.
  • Samsung has a slot that can accept UFS & MicroSD:
  • does using internal storage work differently when processing videos and pictures to when using an external storage to save them? i mean if the speed of the sdcard affects quality then what about the read/write capacity of the phone's internal storage? with sdcards we get the specs listed on the packaging but when it comes to internal storage we just get its actual storage capacity.
  • That is a good question... In fact I'd like Jerry to do another article on transfer speeds within the device and to the external storage card. In computers, there is a vast difference, simply because of internal bus speeds and overall transfer capacity or capability within that 'pipeline' to various devices within that system. That's the short version. I would imagine the same concept applies to phones, but I really can't comment on it... Just guess.... Waiting for another article...
  • In general the phone's internal memory is going to perform better then a MicroSD you insert into a slot. Not all phones but most newer phones especially flagship models, that will be the case. I will acquire ASUS' new ZenFone 3 Deluxe this week. That particular model's internal memory is UFS (universal flash storage) , which is the future of MicroSD beyond current MicroSD. Think of it as a MicroSD with SSD performance. With 256GB internal storage on this highend model, I will store my 4K there and then dump to MicroSD (or computer) for storage and reuse the internal. BTW, where did the author go? He is the one supposed to be answering these questions on his article.
  • For photos etc, the write speed of the card is more important than the read speed. Speed adverts for cards are for the read function. If that same card has a low write speed, not only are you going to waiting forever between shots, you're going to waiting a while to upload your music etc as well. Something to bear in mind.
  • Forever is a really long time to wait.
  • Question: are there any current phones that support the extra speed of UHS-II or faster cards? If not, when can we expect such a phone to come into existence?
  • Very good question. I think it might need support on the actual chip rather then simply the extra connections.
  • I was thinking after reading this, and (not knowing the first thing about writing software) I finally get why high 4K video writing speed is a must. If it's writing directly to the card as you video, would it be forced to buffer and where would the queued up video wait. Surely everything would crash. Or maybe that's only when writing to a physical disk. Anyway.... It would be like the reported 80 mile tailback on a freeway in China that moved at 1 km a day. Just throwing my thought processing out there. You're welcome!
  • I bought a Toshiba 128gb micro sdxc U3 for my Moto Z. Formatted it as internal memory rather than removable storage and got a message saying the card isn't fast enough so performance may be affected. I called Motorola and they said their devices only support U1 cards. Your article says no card can be too fast so what's the issue? How can I get the card to work properly? Any ideas appreciated. Thanks.
  • You need a very fast card to use as adoptable storage so that you won't notice a significant degradation in performance. The Moto Z uses the much-faster UFS 2.0 controller for storage, so the need to have a very fast card is amplified in those cases.
  • I don't recommend anything less than a Class 10 UHS-I card for smartphones.
  • According to the article, UHS-1 is faster than Class 10.
  • My SanDisk card says it's both a Class 10 and a UHS-I card. Class 10 is apparently the max it'll go, so at that point on, you'll want to look at the UHS rating.
  • Superb article. Pixel and iPhone owners miss out on the fun, but they probably don't care (though they should!).
  • Don't forget the Nexus users too. :-)
  • Excellent article Jerry, as usual. Thanks.
  • Bravo Jerry.... Bravo. "Of course, shooting video directly to the phone's internal storage is always better than straight to an SD card." That part right there should be in bold. ;)
  • Great article ... I thought class 10 was the fastest among all.. !!! My bad . Thanks for the article..
  • If write speeds are so important for 4K video then why don't *any* AC SD card buyer's guide consistently mention the write speeds of the cards? Not one SD card buyer's guide mentions the write speeds of each card. The focus is always primarily on cost per GB, and read speeds. Its always hit or miss if the write speed of a card is mentioned (even in cases where the manufacturer discloses its max write speeds).
  • Hence the reason for this article. Hopefully in the future all sponsored sd card articles will have a small blurb and link to this article.
  • I still have a mini sd card for my mpx220. This is a great article I just wish some of these companies wouldn't take out the sd slot. *Cough* Google *choke*
  • Slightly off topic, but for what it's worth, turning on adaptable storage in my HTC One M9 turned out to be a disaster. While I was in San Diego for work training, my SD card failed, and because it was formatted as adaptable storage, I suddenly stopped receiving texts and work emails, because the phone thought the apps no longer existed when the card failed. I reformatted it and turned off adaptable storage, and am now just using my SD card for music and photo storage.