Is U3 the same as V30? And C10, U1, V10?

U3 and V30 are the same — both guarantee 30 MB/s minimum sustained write, just in two different rating systems (UHS Speed Class vs Video Speed Class). Likewise C10, U1 and V10 all mean 10 MB/s. Many cards print both logos for the same speed, which is why it looks like more than it is.

My camera records at 60 Mbps — what speed class do I need?

Mind the units: 60 Mbps (megabits) ÷ 8 = 7.5 MB/s (megabytes), which is inside V10/U1's 10 MB/s floor. So the bitrate alone is covered by V10. Manufacturers still recommend U3/V30 as headroom for multi-channel (front + rear), high frame rates and worst-case sustained writes — pick the class that clears your stream with margin, not the biggest number.

What do A1 and A2 mean, and do I need them?

A1 and A2 are the Application Performance Class — they guarantee random read/write IOPS for running apps (A1 = 1,500 read / 500 write IOPS, A2 = 4,000 / 2,000), both with 10 MB/s sustained write. They matter when the card runs apps or an OS (phones, handhelds, single-board computers), not for plain video recording. A2 also needs host support, or it falls back to lower performance.

SD card speed classes decoded — C10, U3, V30, A2, and the Mbps trap

Pick up a microSD and the label is a pile of symbols: a 10 in a C, a 3 in a U, a V30, maybe an A2, and a Roman numeral for the bus. It looks like five different specs. It's mostly one spec said three ways, plus one genuinely separate number — and one unit mix-up that makes people buy more card than the job needs.

C, U and V all measure one thing

Every Class (C), UHS Speed Class (U) and Video Speed Class (V) marking is a promise of the same kind: a minimum sustained write speed [1]. That's why several of them collapse onto the same value:

Minimum sustained write	Equivalent markings
6 MB/s	C6 · V6
10 MB/s	C10 · U1 · V10
30 MB/s	U3 · V30
60 MB/s	V60
90 MB/s	V90

So U3 and V30 are identical (30 MB/s), and C10, U1 and V10 are identical (10 MB/s) [1][2]. Cards print both logos for the same speed because not everyone knows they're the same — it's not extra performance.

One hardware caveat: the bus limits the class. UHS-I tops out at V30; V60 and V90 require UHS-II or faster [1].

The Mbps trap (this is the one that costs money)

Here's the mistake almost everyone makes. Camera bitrates are quoted in megabits per second (Mbps); card speed classes are in megabytes per second (MB/s). One byte is eight bits, so:

MB/s = Mbps ÷ 8

A 4K dashcam at a generous 60 Mbps is therefore only 7.5 MB/s — comfortably inside V10/U1's 10 MB/s floor. Even most "high-bitrate" single-stream 4K fits under V10 once you do the division. That's why U3/V30 is headroom, not a hard requirement from the bitrate — useful for dual-channel (front + rear), high frame rates and worst-case dips, but not the reason a single 4K stream needs it. Read the camera's spec in Mbps, divide by 8, and match the card's MB/s class with margin. (More on why class ≠ the right card in our selection guide.)

A1 / A2 is a completely different axis

The A1 and A2 marks are not about sequential video at all — they're the Application Performance Class, guaranteeing random IOPS for running apps and operating systems [1]:

Class	Min random read	Min random write	Min sustained write
A1	1,500 IOPS	500 IOPS	10 MB/s
A2	4,000 IOPS	2,000 IOPS	10 MB/s

These matter when the card runs software — a phone, a handheld console, a single-board computer booting an OS — where lots of small random reads and writes decide responsiveness. For a dashcam or security camera writing one big sequential stream, A1/A2 is largely irrelevant; the V/U class is what counts. Note that A2 needs host support to deliver its rated IOPS, or it falls back.

Speed is not endurance

Worth repeating because the labels invite the confusion: every C/U/V/A mark is about speed (or IOPS), never about how long the card lasts. A V30 A2 card can still be a low-endurance consumer card that wears out in months under continuous recording — endurance is a separate spec you choose deliberately (see high-endurance vs consumer).

How to read the label and pick

For video: take the camera's Mbps, divide by 8, pick the V/U class that clears it with margin (1080p → V10/U1; 4K or multi-channel → U3/V30).
For apps/OS storage: look for A1 or A2, and make sure the host supports A2 before paying for it.
For continuous recording: choose endurance grade separately — the class won't protect you from wear.

Bottom line

Most of the label is one number — minimum sustained write — printed in three notations, plus A1/A2 for random IOPS on a different axis. Convert the camera's Mbps to MB/s before you choose, match the class with headroom, and remember the class says nothing about endurance. Tell us the device and the stream and we'll spec the exact class — and the endurance grade to go with it.