How to buy the best SD card for any device
You just want to buy an SD (secure digital) card or microsd card for your DSLR, dash cam, drone, smartphone, or tablet. But one size doesn’t fit all. If the confusing array of memory card logos and specs has you pounding your head against a wall, we understand.
We’ll give you the quick answers for the most common memory card uses. (Pro tip: Check your device’s manual for memory card recommendations.) If your needs are very particular, we’ve also delved deep into SD card standards to help you understand the difference between Class 10, V30, UHS-I, A1, and U3, so you can make the right choice for any device or purpose.
SECURE DIGITAL (SD) CARD CHEAT SHEET
Here are the short answers to determine which SD card to buy for certain purposes:
Best SD card for video use: Concentrate on the Speed Class rating given for your device. Generally, a Class 10 card works for 4K video at 30fps. For anything higher, it’s recommended to invest in V30 and up. See page 96 for more details.
Best SD card for a Gopro Hero: For Hero 4 Black and older, a Class 10-rated card is generally fine but newer cameras such as the Hero 7 Black should be fed with U3- or V30rated cards. See page 97 for more details.
Best SD card for a DSLR: Choose a card based on its maximum write speed. While there’s no logo for that (thank god), 40Mbps to 50Mbps is typically good enough for most consumer and even some prosumer DSLRS. See page 97 for more details.
Best SD card for an Android phone or tablet: Because of limitations in how these devices handle SD storage, storing apps on a card may frustrate you—though an A1-rated card may help a little. For storing photos or video, pay attention to the stated write speed. See page 100 for more details.
Best SD card for a Nintendo Switch: For the best deal, skip the “official” card and buy a high-capacity card that works for your budget. See page 102 for more details.
Best SD card for a dash cam or nanny cam: Ignore the write speeds and X-ratings and go for one that touts “High Endurance.” See page 104 for more details.
SD SPEED CLASS MARKS EXPLAINED
One of the most confusing specs on SD and microsd cards is the dreaded “speed class” mark. For the most part, it’s pertinent only to recording video. Let’s say that again: It’s mostly intended for video.
Unlike with still photography or file storage, an occasional pause in data writes isn’t a big deal, as the camera or device should just pause and pick up where it left off. Video, however, requires undisturbed writes, because the stream can’t be easily paused on
most consumer hardware.
The most familiar of these speed class designations is the basic numeric code of 2, 4, 6, and 10 that have been around since the mid-2000s. The number denotes the minimum write speed without a fatal (for video) disruption. A Class 4 card will write at 4Mbps, for instance, and a Class 10 at 10Mbps.
This was fairly straightforward until the U1 and U3 UHS Speed Class marks were introduced in 2010 and 2013, respectively. U1 and U3 indicate a respective minimum of 10Mbps or 30Mbps write speeds. Both also support a faster ultra-high-speed (UHS) bus.
To help muddy things even more, in
2016, a new Video Speed Class mark was introduced to increase speeds for even higher-resolution cameras and devices. Video Speed Class includes: V6, V10, V30, V60, and V90. As you can guess, the number denotes the guaranteed write speed in Mbps (which in some cases can be lower than a card’s maximum write speed.)
There are actually deeper technical reasons for why you might prefer a Class 10 card (or an even slower Class 6 card) instead of a V90 card for standard-definition video (think 1990s’ era 640x480), but generally, if the card maker did its job, writing even standard-definition video won’t be an issue.
The part that drives consumers batty is that all three speed class ratings are still in active use on memory cards today. Many cards carry multiple speed class markings. Even more confusing are cards like the Toshiba pictured here: If V30 is rated at 30Mbps writes, why does it only have a Class 10 rating, which indicates a 10Mbps write speed?
WHICH SD SPEED MARKING IS THE ‘BEST’?
Believe it or not, the markings on the card and package aren’t there to confuse you, but to help you. Ideally, you’d look at your action cam or nanny cam’s manual, and see that the maker recommends a Class 6, Class 10, V10, or U3 card, and buy a card with that marking.
In fact, that’s the best way to use the speed-class markings properly. The problem is you probably don’t know what your camera or doohickey recommends, so you end up trying to find out what C10, V30, and U1 mean from a browser on your phone while two kids tug on you to go to the toy section.
The only real pitfall to watch for is paying (probably overpaying) for something you don’t need or can’t even use. For example, putting a V30 card in a device that requires Class 10 is about as wasteful as filling up a minivan’s tank with high-octane gas instead of plain, old unleaded.
Seen in that light, the chart below from the SD Association actually starts to make more sense. If you don’t know what your device recommends, you should probably look at the video standard it records at on the right of the chart below, and buy the cheapest name-brand card that corresponds with the speed class. For example, say you have no-name action cam that records at 4K 30fps. Based on the chart below, a Class 10 card should work, with a V10 card being mostly interchangeable. If you have a creepy nanny-cam in your kid’s bedroom that records grainy 1080p 30fps video in night mode, a Class 6 should work just fine.
WHAT’S THE BEST SD CARD FOR A 4K VIDEO CAMERA OR A DRONE?
The guidance above, however, assumes fairly low frame rates of 4K at 30fps, or 1080p at 60fps. It doesn’t actually take into account newer cameras that record at 120fps. Unfortunately, there’s no general guideline, so the fallback is always to refer to the manual or manufacturer’s website. If you don’t know, it’s safest to opt for more speed. For 4K at 60fps, for example, you might want to reach for a faster V30 or U3 card. If you’re recording 8K, surround video, or multiple data streams at once
(GPS data for example), you should opt for a V60 or V90 card.
But again, always check what the manufacturer recommends. You may be surprised at what works. Mavic’s Phantom 4 Pro V2.0 drone, for example, can record at up to 4K and 60fps on a Class 10 card ( go. pcworld.com/cl10)— but it must be
rated at 15Mbps write speeds. So something like Transcend’s High Speed card ( go. pcworld.com/ts63) would work.
WHAT’S THE BEST SD CARD FOR A GOPRO?
As our guidance goes for all devices: Read the manual ( go.pcworld.com/frmn) for what’s recommended for the camera before you go out and buy a memory card. This can save you from buying a card too slow (potentially losing video) or from spending too much money on a card your camera can’t fully exploit.
In the case of Gopro’s popular Hero cameras, much of what is recommended will depend on the vintage of your camera. The very old Hero 3 cameras, for example, don’t support more than 64GB capacity, and with their maximum of 4K video at 15fps, a Class 10-rated card, such as the Sandisk Extreme microsdxc UHS-1 ( go.pcworld.com/sdet) should work just fine.
Step up to the newest Hero 7 Black, which can record 4K video at 60fps, or 1080p at 240fps, and you’ll need a U3- or V30-rated memory card memory card like the Samsung 128GB EVO Select ( go.pcworld.com/smsd).
Gopro’s manual nicely lists cards that it has vetted for each camera going back to the original Hero.
WHAT’S THE BEST SD CARD FOR A DSLR?
There’s a very important thing to remember: The Speed Class discussions above are mostly pertinent to video use, where you cannot ever have the card stall while writing video. Modern digital cameras aren’t so sensitive. If there’s a slowdown while writing 40 images, the camera’s internal memory buffer can hold the pictures just a bit longer while they’re written to the memory card. So, for the most part, even super-budget SD and microsd cards will yield good results for the average photographer.
The only real problem is when that buffer is full from taking, say, 75 images of the kids blowing out the candle. Once that happens, the camera won’t take pictures until the buffer is clear. Sometimes, the camera will actually slow down the picture-taking from 4fps to 1fps while clearing the buffer.
For these photographers, you’ll want to pay attention to the explicit write speed of the
card. The Sandisk Extreme Pro ( go.pcworld. com/sdpr) pictured here, for example, can write at 95Mbps. There is no industry logo or marking for write speed, but we’ve found that most cards that state the write speed are bragging (sincerely) about a tested capability.
If you’re choosing between cards for photography and you have a choice of V30, or V10 (or Class 10), the V30 will likely outperform the Class 10, at least by the specs.
Some card makers will actually express the maximum write speeds as an “X-rating,” such as
400X. This is the write speed of the card expressed by CD-ROM speeds. Every 100X denotes 15Mbps. For still use, you’ll want a higher X-rating if you like to take a lot of pictures in a row.
TESTED: SD PERFORMANCE IN A DSLR
How much does the write speed matter in actual use? We did some quick tests with four grades of Sandisk microsd cards in a Sony Alpha A7R II camera. We timed how long it took the camera to write 10 RAW+JPEG files, each about 42MB. For this test we used a 256GB Sandisk Extreme ( go.pcworld. com/256x), a recent-production 400GB Sandisk Ultra card ( go.pcworld.com/400u), a 3-year-old 32GB Sandisk Ultra card ( go. pcworld.com/32ul), and a nearly generic, basic black 32GB Sandisk card ( go.pcworld. com/32cd). Each card’s markings are noted on the chart below. Only the Sandisk Extreme
had a rated write speed of 90Mbps. Each card was formatted in camera prior to testing.
There are three takeaways from the results you see. The most obvious is that there is a world of difference between the generic 32GB Sandisk card with no markings and the older 32GB Sandisk Ultra card. There’s also a galaxy of difference between the older 32GB Sandisk Ultra card and the new 400GB Sandisk Ultra card. While some of that is the newer memory chips in the 400GB card, some of it is also the capacity. Memory cards today are very similar to SSDS, where some of the capacity is set to cache reads and writes. What that means is a 400GB SSD or memory card, is generally going to be faster than a lower-capacity version of the same model. As the large card reaches full capacity, cache gets smaller as it’s turned into storage, and performance will drop.
Finally, the test revealed yet another factor that comes into play with SD media: the memory bus of your device. We expected the 90Mbps 256GB Sandisk Extreme to blow away the 400GB Sandisk Ultra, which while not specifying its maximum speed rating, is but a U1 card. The fact that the two performed so closely has less to do with the SD and more to do with its host—the camera. The 2015-vintage Sony Alpha R7 II apparently uses a very old USB 2.0 bus coupled with a large buffer, so it can basically never exceed about 35Mbps writes. We know this from extensive testing Alik Griffin ( go.pcworld. com/alik) has done on the Alpha R7 II. Paying extra for 90Mbps would be a waste.
Granted, having a faster card does mean you can move the pictures to your computer much faster, but that’s probably not as important as write speeds in the camera itself.
To confirm our hypothesis about the camera bottleneck, we used a Sandisk UHS-I USB adapter to write a single 6GB 4K video file to each of the cards from a laptop. The 256GB Sandisk Extreme was at or around its rated 90Mbps write speed, while the 400MB Sandisk Ultra wrote at about 40Mbps. The two remaining Sandisk cards were obviously much, much slower, with writes at 10Mbps or
less. Each card was formatted prior to testing, using the EXFAT file system.
The upshot for DSLR photographers focused on still photos is to pay for a card that can write at close to the maximum write speed of your camera. The 3-year-old Sony camera obviously has a serious limitation, but a camera produced in 2018 or 2019 is unlikely to be as hindered. Look for the rated write speed of the card. You won’t always find one, but the good news is, cards that can hit high write speeds usually like to brag about it on their packaging.
WHAT’S THE BEST SD CARD FOR AN ANDROID PHONE OR TABLET?
When it comes to an Android phone or tablet, you can pretty much give up on using speed class or write speeds to choose a memory card. While video cares about uninterrupted minimum speeds and still photography cares about maximum write speed, the designation that concerns running applications from a card is “Application Performance Class,” expressed as Class 1 (A1) and Class 2 (A2) markings.
These specs ratify a minimum sustained sequential write speed of 10Mbps, and more importantly for application use, a minimum random read and minimum random write performance.
This is typically measured in IOPS (input/ output operations per second) and indicates how fast a card can read and write bits from different areas of the memory card.
Unlike video and photo reads and writes, which are mostly sequential, application use from a card tends to jump around. Higher IOPS improves app performance.
TESTED: WHY A1 AND A2 PROBABLY DON’T EVEN MATTER
While memory cards are typically tested in a PC with Windows-based storage tools, we wanted to see if we could detect a difference
in the place the cards would be used: a phone. We used an LG V40 Thinq phone with the Qualcomm Snapdragon 845 SOC running Android Oreo, and Androbench 5.01 to measure the performance of each of the cards—an A1 card, an A2 card, and two cards that lack any such class marking (as noted in the chart on the previous page).
We did not test the cards using Android’s Adoptable Storage ( go. pcworld.com/adpt), as the V40 doesn’t offer the option, nor would it allow Androbench to run its tests. Each of the cards was formatted in the phone prior to use.
The results between the A1 and A2 cards were mixed. In random reads, the A1-rated Sandisk Ultra 400GB came out in front by about 30 percent. In the perhaps more critical random write performance, the A2-rated Sandisk Extreme performed best.
But even there, the Extreme card’s performance was underwhelming. That’s due to the same issue we had in our DSLR tests earlier: the hardware.
Technically, the Sandisk Extreme is rated for almost four times the random-write speed as the Sandisk Ultra, but to achieve that, you need hardware and firmware that fully supports the newer A2 specification.
Today, there are no known Android phones or tablets that support the 2016-era SD 5.01 specification. Even worse for those hoping to use a 400GB microsd card to host apps—today’s phones don’t even support A1 yet.
In fact, the Qualcomm Snapdragon 845 SOC inside the V40 and other premium phones only supports SD version 3.01, which was passed in 2010. The App Performance specs for A1 and A2 were passed in 2016 with version 5.1.
Even worse: We ran Androbench on the V40’s 64GB of Flash storage and saw about 15 times the performance of the Sandisk Extreme in random reads, and about nine times that card in random writes.
The practical upshot is that if you want to store apps on your microsd card and get more performance, an A1 card can’t hurt. It’s likely to have higher random performance than one without a rating, though your phone’s limitations may not allow it to reach its full potential. And yeah, it’s just not worth paying a premium for an A2 card just yet.
The two caveats here are if you want to use the card primarily for storing media for consumption, or for capturing your own videos. If you want to, say, copy 128GB of MP3 and video files to the SD card to watch or listen to, you may want to pay for a card with faster write speeds, such as this
100Mbps Sandisk Ultra ( go.pcworld.com/ sand). This will greatly cut down how long it takes to copy the media to the card on your PC or your mobile device. If you plan to use your device for capturing video on a regular basis, you should probably follow the same guidelines from the video section earlier—a Class 10 works in most cases, such as this Kingston Canvas Select ( go.pcworld.com/kcan).
WHAT’S THE BEST SD CARD FOR A NINTENDO SWITCH?
Nintendo’s own guidance ( go.pcworld.com/ nngd) is to use a UHS-I card with a “transfer speed” of 60Mbps to 95Mbps (UHS-I is not to be confused with the U1 or U3 Speed Class markings, which just mean minimum write speeds of 10Mbps and 30Mbps, respectively). Nintendo also says that “the higher the transfer speed, the better gameplay experience on Nintendo Switch.”
That’s likely meant to lower the load time
of games, which can be fairly large (TakeTwo’s NBA 2K19, for example, is 31.5GB), although the average Nintendo Switch game is under 3GB in size.
Nevertheless, the UHS-I bus supports multiple maximum performance modes: 12.5Mbps, 25Mbps, 50Mbps, or 104Mbps— and it’s unclear which mode the Tegra X1 in the Switch uses. In our tests below, we found very little difference between a Sandisk Extreme with a 160Mbps maximum read speed and our basic Sandisk card with a 45Mbps maximum.
For most gamers, we think it boils down to capacity first with explicitly stated read performance a very close second for the best experience on the Switch. Note: Cards often don’t state their read performance unless it’s worth touting, so if you want to ensure your card doesn’t fall below the maximum potential, you’ll probably end up with something a little overkill in this department.
Since the card is not primarily for video, the Class, U-, and V-ratings don’t matter much. And since Tegra X1 is likely limited to version 3.01 of the SD specification, A1 and A2 ratings aren’t relevant, either.
If you’re a serious Safety Sally, you can go ahead and buy an “official” memory card, such as the 128GB Sandisk Nintendo Switch ( go.pcworld. com/128s). It’s rated for 100MB/S read and 90MB/S write speeds and carries U3 and V30 markings. But it can cost as much as $35 on Amazon. Alternatively, you could save some money by opting for a 128GB Sandisk Ultra card with a 100Mbps read speed—you’d save about $15 and probably never notice a difference.
TESTED: MEMORY CARD PERFORMANCE IN THE NINTENDO SWITCH
Rather than go off our gut instincts we decided to look at one aspect of game experience: level loads. We installed the 21GB game Doom on each of the memory cards used in our previous tests and then timed how long it took to open the level Resource Operations.
We averaged three level loads and restarted the Switch between runs. The results, as you can see, are pretty underwhelming. The four cards used in the tests range from yuck to yum, but the Switch doesn’t care all that much what it eats.
The reason? Level loads for a game aren’t always about sheer read performance. They can often be Cpu-intensive as texture assets and sound assets are decompressed before gameplay can begin.
The basic upshot is that a faster memory card can indeed lower the level loads and game starts, but probably not by much.
WHAT’S THE BEST SD CARD FOR A DASH CAM OR NANNY CAM?
If you just bought a dash cam and are eyeing a card that simply offers the most capacity for the price, you might be making a huge mistake. That’s because memory cards actually have a limited lifespan. While DSLR or action-cam usage is unlikely to hit that limit, a surveillance or dash cam is a different story.
Take your average cheap Black Fridayspecial card and drop it in a dash cam and it just might quit in a few months. In a crash cam or surveillance cam, that’s a disaster.
The answer is a “High Endurance” card, which is purpose-built for heavy use and harsh environmental conditions.
The 32GB Transcend High Endurance card ( go.pcworld.com/32tr), for example, is rated for 6,000 hours of 1080p video before possibly quitting. Endurance on these cards usually increases with capacity, so the same Transcend card at 16GB is rated for 3,000 hours, while the 64GB version is rated for 12,000 hours.
Transcend attributes the lifespan to its use of higher-performance MLC NAND, which is a less data-dense version of memory. Competitors such as Sandisk say MLC isn’t the only answer— firmware and controller NAND matter too. Although Sandisk doesn’t disclose its memory type (we believe it to be 3D TLC) the company’s own 64GB High Endurance memory card ( go. pcworld.com/65en) is rated to live for 10,000 hours, and 5,000 for the 32GB version. Again, the recommended course of action is to buy what your dash-cam maker recommends. If you don’t know, a high-endurance memory card makes the most sense.