- Official Post
There are many different classes etc. for SD cards and here I collect the data over it on one page
First, there was the speed class, which went from Class 2 to Class 10. Then there was the UHS Speed Class, where the cards fall into either U1 or U3. More recently, there’s a newer system, the Video Speed Class, that uses categories like V30, V60, and V90.
And now the SD Association has come out with a new rating system specifically to categorize suitability for SD and microSD cards in application-heavy uses. It’s known as the Application Performance Class Specification, and it’s written in the form of A1 or A2.
So, we start with these first
Application Performance Class
Application Performance Class | Pictograph | Minimum Random Read | Minimum Random Write | Minimum Sustained Sequential Write |
|---|---|---|---|---|
Class 1 (A1) |
| 1500 IOPS | 500 IOPS | 10 MB/s |
Class 2 (A2) |
| 4000 IOPS | 2000 IOPS | 10 MB/s |
Speed Class
Speed Class | Minimum Sequential Write Speed |
|---|---|
2 | 2 MB/s |
4 | 4 MB/s |
6 | 6 MB/s |
8 | 8 MB/s |
10 | 10 MB/s |
UHS Speed Class
UHS Speed Class | Minimum Sequential Write Speed |
|---|---|
1 | 10 MB/s |
3 | 30 MB/s |
Video Speed Class
Video Speed Class | Minimum Sequential Write Speed |
|---|---|
V6 | 6MB/s |
V10 | 10MB/s |
V30 | 30MB/s |
V60 | 60MB/s |
V90 | 90MB/s |
x Speed Factor
Some manufacturers, like Lexar, also set an X Speed on their cards. To better have an overview of them here also a small table about it.
x Speed Factor | Minimum Sequential Write Speed |
|---|---|
100x | 15 MB/s |
120x | 18 MB/s |
133x | 20 MB/s |
150x | 23 MB/s |
200x | 30 MB/s |
400x | 60 MB/s |
600x | 90 MB/s |
633x | 95 MB/s |
1000x | 150 MB/s |
1400x | 210 MB/s |
1800x | 270 MB/s |
2000x | 300 MB/s |
2500x | 375 MB/s |
3000x | 450 MB/s |
4000x | 600 MB/s |
5000x | 750 MB/s |
SD Card Bus Type
But pay attention that there is a UHS bus type too which is not to be compared with UHS speed...
SD Card Bus Type | Maximum Speed |
|---|---|
UHS-I | 104 MB/s |
UHS-II | 312 MB/s |
UHS-III | 624 MB/s |
SD Express | 985 MB/s |
There is a certain amount of backwards compatibility between UHS-I and UHS-II. You can use either card type in any camera or SD card reader that accepts an SD card. The critical thing to understand is that both the device and the SD card must be UHS-II compatible if you want to unlock the additional speed benefits of the UHS-II interface.
Types of SD Card
SD Card Type | Capacity |
|---|---|
SD | 128 MB → 2 GB |
SDHC | 4 GB → 32 GB |
SDXC | 64 GB → 2 TB |
SDUC | up to 128 TB |
What do you need?
At the end we just need to mention what speed you need for what 
I just mention the starting speed - all above is of course better
8k Video → 30 MB/s → U3 → V30
4k Video → 6 MB/s → Speed Class 6
1080p Video → 4 MB/s → Speed Class 4
Standard Video → 2MB/s → Speed Class 2
So, as you see if you only have cards with Speed Class x you can't record 8k videos as example but should be enough, starting at class 6, for 4k videos. Of course, I recommend using U3 / V30 cards for 4k recording to be sure.