by Josh Shaman

SanDisk Extreme microSDXC UHS-I Review

The SanDisk Extreme microSDXC UHS-I is a memory card designed for tablets, smartphones and cameras that ships in capacities of 16GB, 32GB or 64GB and differentiates itself from other cards on the market with its robust performance. SanDisk quotes transfer rates at 80MB/s for read activity and 50MB/s for write activity. These performance specs along with the UHS Speed Class 1 (U1) and Class 10 video recording ratings optimize the Extreme microSDXC UHS-I to handle anything from documents and images to Full HD video at 1080p. This is particularly significant for photographers and video/audio editors who need to capture or edit loads of content, though in typical consumer use cases the card will undoubtedly drastically cut down on transfer time as well.

On top of its performance aspects, the Extreme microSDXC UHS-I is waterproof, shockproof, X-ray proof and can handle extreme temperatures. The card is rated to operate at temperatures from -13ºF to 185ºF, and it can remain operational even after being submerged in salt water a meter deep for 3 days. SanDisk also says the card will survive 16 foot drops and 500G of shock.

So the question becomes that of price. Our 64GB Extreme microSDXC UHS-I review model is priced around 100 bucks. There are certainly cheaper 64GB microSD cards out there, but how many claim 80MBps/50MBps transfers? SanDisk positions this SDXC card in one of their upper echelon segments, "Extreme." They also offer the "Extreme Pro" for power users who require the very top of the line performance, the "Ultra" as a more entry offering for smartphones and tablets, and a fairly pedestrian model for everyday use.

The SanDisk Extreme microSDXC UHS-I is available now at a street price of $30 for the 16GB, $50 for the 32GB and $100 for the 64GB. The cards also feature a lifetime warranty.

SanDisk Extreme microSDXC UHS-I Specifications

  • Form factor: microSDHC (16 GB and 32 GB), microSDXC (64 GB)
  • Available capacities: 16 GB, 32 GB, 64 GB
  • Performance/speed: Up to 80/50MB/s read/write speed (32 GB & 64 GB); Up to 80/30MB/s read/write speed (16 GB)
  • Card dimensions: 0.59 in x.43in x.04in (15 mm x 11 mm x 1.0 mm)
  • Operating temperature: -13ºF to 185ºF (-25ºC to 85 ºC)
  • Storage temperature: -40ºF to 185ºF (-40ºC to 85ºC)
  • Compatibility: Compatible with all microSDHC, microSDXC, microSDHC UHS-I, and microSDXC UHS-I supporting host devices
  • Support: Lifetime limited warranty

Design and Build

The SanDisk Extreme microSDXC UHS-I has the same design as is standard with microSD cards. It is compatible with any microSDHC or microSDXC device.

On the front of the card is the relevant branding and capacity information, and the top half is red while the bottom is gold. The back of the card shows the eight gold pins as well as the circuit board layout. There is also a small black sticker with the model number.


Using our Consumer Testing Platform, we measured transfer speeds from the SanDisk Extreme microSDXC UHS-I 64GB with IOMeter. Sequential read and write speeds measured 89.41MB/s and 58.51MB/s respectively, while random large-block transfers measured 82.10MB/s read and 41.54MB/s write. The read activity figures beat the quoted 80MB/s mark SanDisk provided. Write activity in sequential transfers also proved stronger, though write activity for random large-block transfers didn't quite make it.

Comparing the Extreme microSDXC UHS-I, we stacked it up against the SanDisk Extreme SDHC UHS-I 16GB and the SanDisk Extreme Pro SDHC UHS-I 32GB. For the Extreme SDHC UHS-I 16GB, sequential read and write speeds measured 44.58MB/s and 40.01MB/s respectively, while random large-block transfers measured 42.57MB/s read and 5.93MB/s write.

Rounding out the cards, the Extreme Pro SDHC UHS-I 32GB, sequential read and write speeds measured 89.13MB/s and 73.08MB/s respectively, while random large-block transfers measured 80.91MB/s read and 15.30MB/s write.


The SanDisk Extreme microSDXC UHS-I is designed for high performance applications such as video and audio editing and for consumers who just require more performance from their memory card. On that note, SanDisk rates the 32GB and 64GB model at 80MB/s for read activity and 50MB/s for write activity (80/30 on the 16GB). SanDisk also rates the card to handle extreme environments, and they back up that assertion with their standard lifetime warranty.

In testing, the SanDisk Extreme microSDXC UHS-I 64GB proved to be quite impressive. It had no trouble competing against the full-size SD Extreme (16GB), beating it handily. Even more striking though, is that it also took on the Extreme Pro (32GB) and performed well in comparison. The Extreme microSDXC UHS-I 64GB was marginally better in both sequential and large-block random read activity and significantly better in large-block random write activity. Still, the Pro did outshine the Extreme (64GB) with its sequential write activity. Overall, at the price point and 64GB capacity, the SanDisk Extreme microSDXC UHS-I packs a mighty punch.


  • Higher read activity performance than SanDisk quoted
  • Outperformed the Extreme Pro in three of four tested categories


  • Price point higher than lower performance 64GB microSD options

Bottom Line

The SanDisk Extreme microSDXC UHS-I features a high maximum capacity at 64GB and delivers robust performance, even sometimes exceeding SanDisk's quoted maxes.

SanDisk Extreme microSDXC UHS-I at

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