How to pick a microSD card — reading the spec markings and matching them to use case

2026 update: ported from the old VuePress blog. The SD Association’s marking system hasn’t really changed since the original publication date, but I’ve revised the 2026 view of capacity-tier pricing and the state of SDUC (over-4TB) cards reaching the market. Specific product links should be re-checked and swapped to current models before going live.

When you go to buy a microSD card, the cards on the shelf have an alarming number of markings on the face. “SDXC”, “U3”, “V30”, “A2”, “I”. Two cards of the same capacity can differ in price by a factor of two. Which one to buy?

This piece sorts out how to read microSD markings and lays out the minimum spec by use case — phone, mirrorless camera, GoPro, Switch. By the end, the time spent staring at the shelf should drop to zero.

The short answer — read capacity and speed separately, let use case set the floor

Short answer: microSD performance is set by three layers — capacity class (SDHC / SDXC / SDUC), speed class (Class / UHS / Video Speed Class), and bus (UHS-I / II / III). Looking at any one of them in isolation isn’t enough to decide.

Minimum spec by use case:

• Phone (Android): 128GB / A1 / UHS-I
• Mirrorless stills + burst: 64GB or more / UHS-II card and body
• GoPro / action cam 4K: 128GB / V30 / UHS-I U3
• Switch / handheld game consoles: 128–256GB / UHS-I (capacity matters more than speed)
• Dashcam: 64–128GB / High Endurance models

Put differently: once the use case is fixed, you only have two or three markings left to read.

Capacity class — SDHC / SDXC / SDUC

Short answer: capacity class tells you the maximum capacity the card supports, and ties into compatibility with the device. If the device is recent, you mostly don’t have to worry about it.

There are three generations (citation needed: SD Association official spec):

• SDHC: over 2GB up to 32GB
• SDXC: over 32GB up to 2TB
• SDUC: over 2TB up to 128TB

Glossary

SDHC / SDXC / SDUC specify a pair: the card’s capacity ceiling and the filesystem it uses. SDHC is FAT32, SDXC is exFAT, SDUC is also exFAT. Drop a newer-generation card into an older device and it may not read because the filesystem isn’t supported.

Compatibility: older devices are narrower

Device support is backward-compatible only, not forward-compatible. From around 2015 onward, SDXC support is basically standard, so this rarely causes friction.

As of 2026, SDUC cards are just starting to appear on the market, and there aren’t many cases where you’d actually want a card over 4TB. For general use, the SDXC range (64GB–1TB) is enough.

Speed class — Class / UHS Speed Class / Video Speed Class

Short answer: speed class is a guaranteed minimum write speed. There are three families — Class (old), UHS Speed Class (U), and Video Speed Class (V) — with newer ones being more strictly defined.

It’s easy to muddle, but all three are about the floor (“never drops below this”), not the ceiling. The number matters most for use cases like video recording, where a stall is a real problem.

What “speed class” means

A guarantee from the SD Association on the minimum sustained write speed. “Class10”, “U1”, and “V10” are three different notations for the same 10 MB/s minimum. In some cases the markings are just different labels on the same performance.

How the three families line up

As of 2026 the cards on store shelves are almost all U1 / U3 / V30 / V60 / V90. The older Class 2–6 cards have mostly disappeared.

The bus interface (UHS-I / II / III) is a separate thing

Where speed class guarantees a floor, the bus interface (the row of pins on the back of the card) defines the ceiling.

• UHS-I: theoretical max 104 MB/s (citation needed: SD Association)
• UHS-II: theoretical max 312 MB/s
• UHS-III: theoretical max 624 MB/s

UHS-II and above add a second row of pins on the back. If the device’s slot isn’t also UHS-II, the speed falls back to UHS-I levels. Phones, GoPros, and entry mirrorless cameras usually cap at UHS-I.

Application Performance Class (A1 / A2)

Short answer: a spec for Android phones that keep apps on the SD card. On top of the minimum sustained write speed, it defines a floor for random I/O (IOPS).

Sustained speed is identical, but A2 is faster on lots of small-file operations (citation needed: SD Association A2 spec). If you’re moving apps onto the SD card, A2’s upside is easier to feel. That said, A2’s real gains depend on a caching mechanism on the device side, and on Android devices that don’t implement it you may not feel any difference from A1.

Picking capacity — a realistic floor by use case

Short answer: pick capacity by the band with the cheapest cost per GB, not by “the most I could ever use”.

Cost per GB usually bottoms out in the mid-capacity range (128–256GB). The price gap between 32GB and 128GB is often only a few hundred to a thousand yen, so when in doubt, you rarely lose by going bigger.

Targets by use case

• Phone (photos, video, music): 128GB floor, 256GB for headroom
• 4K video recording (GoPro / camcorder): 128GB is about two hours (4K60p, 100 Mbps bitrate estimate / citation needed: each manufacturer’s spec)
• Mirrorless RAW burst: 64GB is about 1,500–2,000 shots (24MP RAW estimate / citation needed: depends on camera body)
• Switch / handhelds: 256GB holds roughly 20 downloaded titles
• Dashcam: 64–128GB in a High Endurance variant. Standard cards wear out on write cycles

Comparison: minimum spec at a glance, by use case

Recommended microSD cards

The picks below reflect the direction at the time of writing. From a 2026 vantage point, verify the current model in the same price band before linking.

Phone / Switch — 128GB / A1 / U1

A generalist baseline. As long as it meets A1 and U1 with 128GB or more, daily use is covered. SanDisk Ultra, Samsung EVO Select, and Kingston Canvas Select Plus are the usual suspects.

GoPro / 4K video — 128GB / V30 / U3

Pick a card that clears V30. Choosing one that’s on GoPro’s official compatibility list makes it easier to dodge edge-case issues. SanDisk Extreme and Lexar Professional 1066x are common picks.

Mirrorless burst — UHS-II / V60–V90

Assumes the camera body itself is UHS-II. The card speed maps directly onto how long the burst buffer takes to clear. Price is two to three times a UHS-I card.

FAQ

Q. 32GB or 128GB — which should I buy if I’m undecided? A. If undecided, 128GB. Cost per GB bottoms out in the mid-capacity range, and the price gap from 32GB is usually a few hundred to a thousand yen. The bigger risk is running out of room for video or apps.

Q. How do Class10, UHS-I U1, and V10 differ? A. All three mean a minimum write speed of 10 MB/s — just in different notations. Class is the old standard, U was defined for the UHS bus, and V was defined for video. Cards on the shelf today mostly use the V or U markings.

Q. What does a Nintendo Switch need? A. Switch officially recommends a UHS-I microSDXC. Capacity matters more than speed class in daily use, so a 128GB–256GB UHS-I U1 / U3 is plenty (citation needed: Nintendo official support).

Q. Does a more expensive UHS-II card actually run faster? A. Not unless the device has a UHS-II slot. Phones, GoPros, and entry mirrorless cameras top out at UHS-I. UHS-II earns its price on mid-to-high mirrorless bodies doing burst shooting, and on 8K camcorders.

Wrapping up

microSD markings stop being confusing once you read them in three layers: capacity class / speed class / bus.

Fix the use case and the required spec narrows quickly. Phone: 128GB + A1. 4K video: 128GB + V30. Mirrorless burst: a UHS-II card. Switch: capacity first. Going the other way — buying “the fastest one” without a use case in mind — is the classic way to overpay for performance the device can’t actually use.

When you’re staring at the shelf, narrow your use case to one first. The marking decoder comes after.