Picking a microSD Card

Picking a microSD Card


Updated: 2021-06-19

Like some of you, I don’t buy a new SD (secure digital) card every other week. So, when it comes to purchasing time how do you know you’re getting the right tool for the job? There are tons of wordy articles out there, so we’ll get to the point!

Please note, this article is a quick assist guide on microSD cards and not the other SD card variants. For more in depth, check out the official documentation.

Choose the Right Tool For the Job

When picking a card always do it with a purpose in mind. The average user probably wants extra storage space, but you’re not the average user. Getting the wrong card is like putting crap gas and dollar store oil into your new sports car.

First, ask yourself, what are you going to use this card for?
This will assist with choosing the correct drive space, and speed

Secondly, should we get an SD or microSD? Just get the microSD if you’re dealing with small electronics.
This is the most transferable between devices when repurposing it. You can always put it into a full-sized SD case, phone, Raspberry Pi, USB stick, drone, etc.

Reading the Label

Welcome to the pinch-point! Getting the prettiest label with fancy colors doesn’t mean it’s good.


SD (SDSC)Standard Capacity2 GB
SDHCHigh Capacity4 GB – 32 GB
SDXCExtended Capacity64 GB – 2 TB
SDUCUltra Capacity2 TB – 128 TB
Card Sizing Chart

Class – Bus, Speed, Video, Application

The Speed Class Rating logos guarantees a minimum rate at which data can be written to the card. There are up to 4 different variants of Speed Classes that you can encounter here, Bus, Speed (C or UHS), Video (V), and Application (A); sometimes with up to 4 appearing on the label at once. Wait, four? Yes, The original Speed Class (C) and UHS Speed Class (UHS-I and UHS-II)

A few of the logos can look like the following:

* XC
* UHS-1
* UHS Speed Class 3
* XC
* Speed Class 10
* UHS-1
* UHS Speed Class 3
* Video Speed 30
* HC
* Speed Class 10
* UHS-2
* UHS Speed Class 3
Sample Card Badges

Bus Speed Class

The Bus logo is easily distinguished by the Roman numeral I, II, or III, as well as “EX” or “EXPRESS“.

Bus InterfaceBus LogoBus Speed (duplex)
UHS-II* 50 MB/s (half,full)
* 104 MB/s (half)
UHS-IIII* 156 MB/s (full)
* 312 MB/s (full)
* 624 MB/s (full)
UHS-IIIIII* 312 MB/s (full)
* 624 MB/s (full)
SD ExpressEX
* 985 MB/s (full)
* 1969 MB/s (full)
* 3938 MB/s (full)

Speed Class

Under the Speed Class ratings, we’ll encounter up to three different series of symbols. Classic Speed (C), UHS Speed, and Video Speed Class. This informs you of the minimum sequential writing speed.

Minimum write speedSpeed ClassUHS SpeedVideo Speed
2 MB/s Class 2 (C2)
4 MB/sC4 Class 4 (C4)
6 MB/s Class 6 (C6)Class 6 (V6)
10 MB/s Class 10 (C10)U1 UHS-1 Class 1 (U1)Class 10 (V10)
30 MB/s Class 3 (U3)Class 30 (V30
60 MB/sClass 60 (V60)
90 MB/sClass 90 (V90)

Ultra High Speed Speed Class

As an example, UHS-3’s minimum 30 MB/s write performance is recommended for 4K video.

Source: https://www.sdcard.org/consumers/about-sd-memory-card-choices/speed-class-standards-for-video-recording/

Application Performance Class

So what about the A1 and A2 ratings? It’s a newer rating system specifically for application-heavy uses.

The specification is written in form of A1 and A2 which informs the users of the random read/write speeds, presented in the table below in the form of IOPS Input-Output Access Per Second. So why do we care about “random” read/writes? As we all know, apps don’t store information in a clean linear fashion, information gets fragmented quickly over time.