Our SanDisk Extreme SD UHS-I V3 tests saw write speeds live up to its claims, matching them almost exactly at 71.6MB/s. But as with most other cards on this list, the read speeds leave a bit to be desired, coming in at almost half the claimed speed, 71.6MB/s. All can be forgiven, though, bearing in mind the extremely low cost of these cards, especially while still offering such high capacity to users at up to 256GB sizes. Our stand-out best SD card is the Transcend SDXC UHS-II U3. With a Class 10, V90, U3 and UHS-II rating, we thought it would be fast enough to capture almost anything modern devices could throw at it, but we weren’t expecting the speed results we got. The Transcend did superbly in its speed tests, excelling the claimed write speed (180MB/s) with a whopping 224MB/s, but falling slightly short on the read speed with 224MB/s. Overall, that makes this card an impressive buy at a reasonable cost. This card is ideal for high resolution, rapid-fire stills photography and 8K video, with 4K and HD video being recorded comfortably, too.

There are three main types of SD card: SD, SDHC (high capacity) or SDXC (extended capacity). SD cards typically offer 128MB to 2GB in storage capacity, too small for today’s modern cameras with higher resolutions. SDHC bumps this up from 4GB to 32GB, useful for most photographers and videographers. SDXC cards, meanwhile, range from 64GB to 2TB and are aimed at professional-level users who require more memory. While the higher capacity cards increase in price exponentially, the 633x appears in sizes as small as 16GB, making it suitable for a wide range of photographers and videographers alike who require all kinds of capacities for casual or professional use. We found its write speed to be a little slow compared to other UHS-I cards in this class range, but it’s good value for money and the V30/U3 class listing means it’s still suitable for up to 4K UHD video recording.SD cards are flash memory, which means they have no moving parts and instead rely on electronic chips to store data. While they don’t require power to store data, they can be damaged via water, fire and physical pressure. Some companies offer bespoke 'tough' versions that can withstand these elements, even remaining safe in extreme temperatures, so it's worth looking for those if you're going on an adventure. Actual transfer speeds under our testing churned out a write speed of 33MB/s and read speed of 82MB/s; not too bad, but the write speed is close to the minimum V30 classification on the label, so that's worth bearing that in mind if write speeds are important to your work. Card classifications like V30 or U3 are just categorizations of these speeds. There are three main classes: Speed Class (denoted with a number in a circle), UHS Speed Class (a number in an open beaker-like icon), and a Video Speed Class (V followed by a number). The numbers indicate the minimum writing speed when put under data transfer. Speed class is categorized into Class 2 (a minimum write speed of 2MB/s), Class 4 (4MB/s), Class 6 (6MB/s), and 10 (10MB/s). Choosing the best one for your camera depends on your camera's resolution, buffer size and burst shooting speeds. An additional clue is the UHS Speed Class rating, which is U1 or U3. U1 means it can write a minimum of 10MB/s (like Class 10), while U3 pushes the write speed up to a minimum of 30MB/s. More interested in shooting video? The Video Speed Classes are V6, V10, V30, V60, and V90, with V6 suitable for standard definition video recording and V90 capable of 8K video capture. 4K UHD video recording will require a minimum of V10 ideally, and HD video can utilize V6 or below at a push. How we test SD cards