We researched 30 microSD cards that are new or have been updated since the last batch of eight cards we tested in 2017. We tested both the 64 GB and 128 GB versions of the Samsung Evo Select; the SanDisk MicroSDXC Card for Nintendo Switch, SanDisk Ultra, Ultra Plus, and Extreme Pro; Kingston Canvas Select, Canvas Go, and Canvas React; and the 64 GB models of the SanDisk Extreme, SanDisk Extreme Plus, and the Lexar 633x.

Using a Kingston USB 3.0 High-Speed Media Reader in a desktop PC’s USB 3.0 port, we ran CrystalDiskMark, a benchmarking program designed to test sequential and random speeds on solid-state storage. We ran each test three times and averaged the results. Between each test, we reformatted each card using the recommended utility from the SD Association to stabilize performance. We also tested each card’s sequential and random speeds on a Samsung Galaxy S9 using A1 SD Bench. (You can read more about how the benchmark works at the A1:dev website.)

Every card we tested had consistent performance between runs, but not between devices. Sequential speeds and random write speeds were higher with CrystalDiskMark on the desktop than with A1 on the Galaxy S9, while the A1 benchmark recorded consistently higher random reads. You're much less likely to be running apps or loading game data from microSD on a computer, so we paid more attention to A1 random results than CrystalDiskMark's. Conversely, the desktop PC was able to run the cards closer to their sequential speed limits; the Galaxy phone bottlenecked them, so we paid more attention to CrystalDiskMark than A1 for sequential speeds.

Sequential read speed indicates how fast long swathes of data can be read from the memory card—for example, when you’re watching a movie stored on the card, loading a game level, or copying photos or videos from the card to your computer. Sequential writes are important when putting big chunks of data onto the card: recording a video, shooting pictures, or downloading a movie or a game to your device. All of the cards had sequential read speeds around 90 to 95 MB/s, about the limit of the UHS-I bus, in our CrystalDiskMark testing. Sequential writes were a bit more varied; most cards did fine, with results between 70 and 85 MB/s.

Since microSD cards are mostly used for media storage these days, sequential speeds matter more, but random access speed is still important. Apps often save data in small chunks scattered across the storage device, so a microSD card used for operating systems, applications, or games needs to be fast at reading and writing small bits of data (often around 4 KB) in random locations. Most Android devices no longer let you run apps from external storage, but if your operating system and programs live on the card (as in a Raspberry Pi) or you’re playing a game downloaded to it (as on a Nintendo Switch), it’s important that your random read and write speeds don’t hold you back.

Among the 128 GB cards, random read performance in A1 ranged between 9 and 11 MB/s. Random writes were slower (as they always are) and between 1.5 MB/s and 2.6 MB/s. The Kingston Canvas cards dominated both random read and write speeds; they’d be good choices for running applications from, but their sequential speeds, which are important for reading and writing media, were slower than those of the Switch and Evo Select cards.

In our smartphone random speed tests, the 64 GB cards we tested were faster than their 128 GB counterparts. The 64 GB Nintendo Switch, SanDisk Extreme, and Extreme Pro dominated here, while the Samsung Evo Select had among the best random reads but the worst random write scores of any card we tested this time. All of these are still fast enough; we haven’t experienced or seen reviewers complaining about performance except when looking at benchmarks.

CrystalDiskMark’s random results were a little different; the Evo Select cards fell in the middle of the pack instead of dead last, and Kingston’s trio of Canvas cards—the Canvas Go, Canvas React, and Canvas Select—were right at the top. If you’re buying for a Raspberry Pi or other use where you’ll be doing a lot of random writes, they’re great options.