I was halfway through a portrait session last spring when my camera started stuttering. Not overheating, not a lens issue. The buffer was filling up faster than my card could clear it, and I was shooting bursts of a toddler who had approximately a four-second window of cooperation at any given moment. I missed the shot. It was a cheap card I’d grabbed at a drugstore checkout, and I knew better. That one afternoon cost me more in frustration and missed frames than any card upgrade ever would have.

Memory cards are the most boring purchase in photography and one of the most consequential. Nobody posts unboxings of SD cards. There are no YouTube reviews with dramatic music. But use the wrong one and you will feel it.

Why Your Card Speed Actually Matters (and When It Doesn’t)

The number printed on a memory card is not straightforward. Manufacturers advertise the read speed, which is how fast data moves from the card to your computer during import. That number is almost irrelevant while you’re shooting. What matters is write speed, which is how fast your camera can push data onto the card in real time.

Most cameras write files sequentially into a buffer, a small chunk of internal memory, and then flush that buffer to the card. If your card can’t keep up with the flush rate, the buffer fills and your camera locks up. This is what happened to me. A card with a 95 MB/s read speed and a 30 MB/s write speed looks fast on the shelf but performs like molasses during a burst sequence with RAW files.

For reference, a compressed RAW file from a mid-range mirrorless camera sits somewhere between 20 and 35 MB. Shoot a 10-frame burst at 30 frames per second and you’re pushing 200 to 350 MB through that pipe in under half a second. A card with a 90 MB/s write speed handles that. A card with a 30 MB/s write speed does not.

Decoding the Speed Labels Without a Decoder Ring

The SD card spec system is genuinely confusing, and I think some of that confusion is intentional. Here’s what you actually need to know.

UHS Speed Class is the one that matters most for stills. UHS-I cards cap out around 104 MB/s bus speed. UHS-II cards can hit 312 MB/s but require a camera with a UHS-II compatible slot to get that speed, and they cost noticeably more. If your camera doesn’t support UHS-II, you are paying for nothing.

The Video Speed Class (V30, V60, V90) indicates minimum sustained write speed. V30 guarantees at least 30 MB/s. V60 guarantees 60 MB/s. V90 guarantees 90 MB/s. For most photographers shooting 20 to 45 megapixel stills, V60 is the sweet spot. V90 is worth it if you’re shooting high-bitrate video or using a camera body that can actually saturate the card.

A UHS-I V60 card does not exist because UHS-I can’t sustain those speeds. If you see that label, someone is marketing incorrectly or you’re misreading it. V60 and V90 cards are always UHS-II.

What Cards I Actually Recommend at Different Price Points

I keep a running comparison of cards I’ve tested across different cameras, and my current recommendations haven’t changed much in two years because the market is fairly stable.

For most APS-C mirrorless cameras and DSLRs with UHS-I slots, the Lexar 1066x 128GB runs around $25 to $30 and delivers consistent real-world write speeds between 75 and 90 MB/s. It handles 30 fps burst shooting without buffer issues on cameras like the Sony a6400 or Fujifilm X-T30. That’s where I send most people.

For full-frame mirrorless bodies with UHS-II slots, the Delkin Devices Black 128GB sits around $80 to $90 and is one of the more reliably fast UHS-II cards at that price. The Sony Tough series is excellent but adds a premium for the ruggedized housing that most people don’t need unless they’re shooting in serious weather regularly.

For CFexpress Type B, which is now standard on higher-end bodies from Nikon, Canon, and Sony, I’d spend $100 or more on a 128GB card from ProGrade or Delkin. This is not the place to buy a no-name card. The failure rate discrepancy in this format at the budget tier is real, and CFexpress recovery is expensive.

The Time I Spent More on Research Than the Card Was Worth

I got into the deals side of gear coverage after a specific moment. I had spent about four hours cross-referencing card benchmarks before a weekend trip, tabs everywhere, manufacturer specs against third-party tests. I saved $11. That was the version of me who needed to get more efficient.

Now I run a much simpler filter. First question: does my camera support UHS-II? If no, buy a UHS-I V30 or faster card from Lexar, Sandisk, or Kingston and stop thinking about it. If yes, and I’m shooting heavy bursts or high-bitrate video, I step up to a UHS-II V60 minimum. I don’t chase the fastest card available, I chase the card that won’t become my bottleneck.

The other thing I check is the card’s warranty. Lexar and Delkin both offer lifetime limited warranties. That matters for a component you’ll use on every single shoot.

Don’t Buy More Card Than Your Camera Can Use

The right memory card is one that matches your camera’s interface, meets your write speed needs, and doesn’t charge you for headroom you’ll never access. A $120 V90 UHS-II card in a camera with a UHS-I slot performs identically to a $25 UHS-I card because the slot is the hard ceiling, not the card.

Buy the card that fits your slot, clears your buffer, and keeps shooting. Everything past that is just a number on a package.