What the real speed of class 4 microSD should be?

Hi. Im running some speed tests on my new sandisk microSD 16 GB class4. While using for tests H2testw I’m getting:

  • read speed 3,87 MB/s
  • write speed 8,39 MB/s

While simple copying file using teracopy to / from disk the speed is about

  • read 4,5 MB/s
  • write 9 Mb/s

the capicity itself looks fine - 16GB ok.

My question is: is this speed not to slow for 4class microSD card? I used also other software to check the speed and never got over 4MB/s. Can someone who has this card tell me what kind of speed is he getting? I want to be sure i have the genuine one.

screenshot from H2testw:

and card itself:

As I understand it, the speed rating or class of card refers only to the speed of _ writing data _ to the card, not the speed of reading data from it.

So if you’re getting 8 & 9mb per second, that’s twice the rated speed of the card. I wouldn’t complain.

I’ve used H2testw before to test my cards and the results are different depending on whether or not you have files on the card when you’re running the test and whether or not the card is in a device (like a sansa player) or in a card reader.

From what I understand, the most accurate results are achieved when the card is formatted first and it’s placed in a card reader when the test is run.  If it’s in a PMP or there are files on it, you may get a slower read/write speed. 

For a class 4 card, the only regulated requirement is that the write speed has to be a minimun of 4mb/s. 

I just got  mine in the mail today, and I ran the H2testw. FYI I’m running Windows Vista Ultimate 64-bit (i’m mentioning because your pic looks like you’re on XP), and using a Sanisk MobileMate Reader. The MicroSD Card looks exactly like mine. Here are the results of the H2testw:


15185 MByte

48:14 min

5.25 MByte/s


15185 MByte

26:40 min

9.49 MByte/s

The Capacity, as you stated, seems correct. The Windows Hard drive properties list shows 14.8 GB  total space. 

4MBytes/s should be the minimum speed, and the average should be equal to or higher than that.


Sandisk sells class 4 versions of microSDHC cards in the US as “Mobile Ultra microSDHC”. I didn’t find the specific one we have on the SanDisk US website, but I did see it on the SanDisk’s China Website (Item # for my card, on the back side of the packaging, is SDSDQ-016G-P36M) and its states it as a class 2. Search the Item number on your packaging and see where it gets you.

I’ve been transfering  differrent files, and so far I have not encountered lower than 5MByte/s on my card. If your card is similar to mine, it’s possible that it is faulty, not phoney. Unless I just got a good fake one.