Most people should skip the spec sheets and start with their device's manual. Find the card type and speed label your camera, drone, phone or console says it needs. Buy a card from a brand you recognise, sold by a retailer you trust, that carries that label. Then stop. A faster label than your device needs mostly buys flexibility: the SD Association's guide to choosing the right speed class notes that a faster card gives you room to use it in other devices.
Match the symbol on the card to the symbol in your manual
SD and microSD cards carry several small symbols on the front. Each one is a separate rating, and each matters for a different job:
- Video Speed Class: a V followed by a number, such as V30, V60 or V90.
- UHS Speed Class: a U with a number inside, such as U1 or U3.
- Application Performance Class: A1 or A2. Look for this if your phone or handheld runs apps or games from the card.
- Bus interface: UHS-I, UHS-II, or SD Express and microSD Express. This only matters if your device supports the faster interfaces, covered below.
The match is what matters, not the biggest number on the shelf.
The SD Association's site explains what each class means in its post on choosing the SD speed class that's right for you, and covers why new ratings were added over time in the evolution of SD ratings for new applications. If a retailer listing disagrees with them, trust the SD Association's pages.
What to ignore on the packaging
Many cards print a big "up to" speed on the front. The SD Association's post on the evolution of SD ratings advises focusing on minimum sustained speeds rather than maximum speeds, so look past that headline figure.
UHS-II and SD Express: pay for them only if your device supports them
A UHS-II or SD Express card only shows its extra speed in a slot and reader built for that interface. If your manual doesn't mention UHS-II, SD Express or microSD Express, you don't need to pay for it.
In October 2023 the SD Association announced the SD 9.1 specification, which, per its own announcement, introduces new speed classes and performance features.
Not everyone was convinced. PetaPixel ran a piece the same month arguing that SD Express got an update but it still won't make the format work.
My recommendation
Open your device's manual, write down the card type and the class symbols it asks for, and buy a name-brand card with exactly those symbols from a retailer you trust. When in doubt about what a symbol means, the SD Association's own pages are the final word.
