Understanding SD Card and Speed Classes

Understanding SD Card Symbols

SD Card Association classify the storage sizes or storage capacity of your SD Cards  into (3) Types :

SD => If you see only the SD symbol it means it can only store 2GB of data and below. You can only store 1 complete movie or (more or less) 400 mp3 songs.) SD is an acronym for Secure Digital.

SDHC => If your SD Card is an SDHC  or Secure Digital High Capacity it can store up to 32GB of data and below. (You can store more or less 32 complete movie for this capacity.)

SDXC or Secure Digital eXtended Capacity =  you can store up to 2TB (Terrabytes) of data.

Note: SDXC requires a special formatting called exFAT filesystem. exFAT has been adopted by the SD Card Association as the default file system for SDXC cards larger than 32 GB.

SDXC Yes Yes Yes
SDHC No Yes Yes
SD No No Yes

Understanding Speed Classes

Now, let’s talk about SD Card Speed Classes. The SD Card Association defines card speeds using two terms: Speed Class and UHS Speed Class.

Speed class is the original rating used and the number defines the card speed; 4 for 4MB/s, 6 for 6MB/s. etc.
UHS (Ultra High Speed) uses minimum write speeds to differentiate the cards; UHS-I Speed Class 1 has a minimum write speed of 10MB/s while UHS-I Speed Class 3 has a minimum write speed of 30MB/s.

What does it mean by Class 10 SD Card?

So if you’ll gonna look at the table below, Speed Class rating is ranging from CLASS 2 (slowest) and Class 10 (fastest). It can transfer or write data to your SD Card at a 10MB/s (Megabytes per Second). If you’ll transfer a regular mp3 song to your SD Card, it will take only less than half a second to save it. Because MP3 song usually range between 3MB to 5MB in sizes.


UHS-I Speed Classes

There’s also a separate, even faster techonology called UHS I Classes  (for Ultra High Speed), but most current devices can’t use them. Let’s look at the table below:


Most of today’s devices now supports UHS I Speed Classs as standard for reading and writing data.

You might ask, is Class 10 SD Card compatible with UHS I Speed Class  compliant  devices?

ANSWER: As long it has the above UHS I symbol, you are assured that it will work with your UHS I devices.

The above Speed Class and UHS Speed Class symbols indicate minimum transmission to ensure smooth writing of streaming content such as video recording. This is very relevant for camcorders, video recorders and other devices with video recording capabilities.

I hope I have decrypted the mysteries everything about SD Card sizes and speed classes. If you have further questions please feel free to comment below, I’ll make sure to answer these the soonest possible.  Thanks and have a good day!



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