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My SD Card is too SLOW!?

This was the question that was posed, and there seems to be some mystery at all these numbers all over the cards you have (or maybe there are no numbers at all).

I want to break down these numbers and make it easier for you to decide what you need to take photos or videos.

There are 3 Categories of numbers you want to look for on your cards:

Speed Class
UHS Speed Class
Video Speed Class

These aren’t exactly clear, but with this little guide, you’ll be able to find them, and understand them.  Most importantly, you’ll be able to pick a card based on your needs.

Speed Class is the first number you will see, and these days… if it’s not a 10 here, DON’T BOTHER. I say this because Speed Class is a bit Antiquated, that was the old system, and the number corresponds to the Minimum write speed of the card.  So if you see a 2 or 4, you are left with only having a 2 or 4MB/sec minimum write speed. 

What even is happening here? Speed Class 4? (seen with the 4 inside a giant C)

This means as you start cranking out 15MB photos, it’s going to start writing them to the card at 4MB/sec at bare minimum. Sure the speeds could be a bit faster, depending on your camera, your file sizes, and if you prayed to the gods of image compression and technology expedition. But, in most cases, you’re going to see that card being worked hard as you fire off a burst of photos. 

Oh, you want to record video? I mean, you can, it’s just going to be the size of a postage stamp, it won’t even be 720p video.

This brings us to the next rung of numbers you’re going to see. 

UHS or Ultra High Speed Speed Class. (Listen, I didn’t come up with the terminology for this stuff). UHS Comes in 2 major flavors, 1 and 3 and comes in 3 secondary flavors, Class I, Class II and Class III.

This gets confusing easily. 3 32GB cards all saying different speeds? All Class 10? BUT, one is only UHS 3, can you tell which one? That’s right, the one with the 3 in the U. (Also wtf SanDisk, why did you label these 30 and 40 MB/s when they were the same card)

What you need to know is this.  We live in a newer world of technology, and you probably have a digital camera, DSLR, or Video Camera that can shoot high quality images, very fast.  You will want to skip over UHS 1 (which will generally not even have a roman numeral), because these will cap out of about 25MB/sec transfer rates. Your starting point for photography on a card’s speed should be:


You might think that you don’t need a huge amount of speed like that in your camera. You might even be right. But, you can get these class of SD cards that will provide write speeds at a minimum of 30MB/sec. This will make sure you don’t have any “traffic jams” trying to take photos. Or worse, shots being thrown out of the buffer completely and not writing to the card at all.

Video Class Speed is a new speed class that will start to pop up on the radar of SD cards and all flash type media.  If you’re shooting video, at least HD / Full HD video, you’re going to want that same UHS-I 3 card, and you might find a new number on the card itself.

In this case, I have a V30.

V30! Good for Full HD and some shorter lower bitrate 4k. But stick to 1080p if you’re doing video.

V30 is plenty of bandwidth to record Full HD video, but it might struggle in recording 4k Video because of the amount of data used in pushing to the card. 

This is where the price points for these cards start jumping up astronomically and if you’re not doing 4k or even 8k video, you really don’t need a UHS-III V90 Card pushing 624MB/sec, but hey, you do you.

So, now you have the beginnings of knowledge on these numbers for your cards, what do you want to buy?

You will want to get at minimum UHS 3 if you’re doing photos, you have to think, if you are firing off a few shots, the camera has to buffer and write 10 – 15mb of data each shot. 

So, if the card is UHS 1, Class 4, or whatever. You’re going to generally going to write an image at a minimum 10MB/sec on a UHS device or 4MB/sec on a standard device. 

Your camera and it’s write speed and buffer make the difference too, if it’s pushing 40MB/s on burst shots, it’s going to take a while to write data on a card that most likely will run at 10MB/s depending on your camera body’s internal buffer/memory to write etc. And then, you start to lose photos.

That being said,

Finding a UHS 3 Class 10 card is easy. 

Here is the one I generally have a large pile of.  Cheap, reliable for the most part, and easy to come by.

Now what drives up prices on these cards (as I explained earlier) isn’t the write classes, is the Sustained Speed VClass.


These cards are ok, at V30 for video, 30MB/s is fine for a 1080p video, but kind of is pushing it for 4k. 

Now, if you want to jump from Sandisk (they are cheap, you can buy them in bundles, but will break physically over time, the chip will still have the information, but the rest of the housing will fall apart)

Go, Lexar Professional Line.

These are really durable and amazing cards. But, you will pay for them.

I had 64gb Lexar CF and SD cards Where the max speed is 160MB/s and the Guaranteed speed is 150 MB/s and you pay the price for them (though the CF cards are roughly the same nowadays as Sandisk price wise).

A word of warning though, due to a lot of dickheads on the internet, people buy the UHS-II casing for the cards and put UHS-I chips in it. Or even just slap the stickers on the card.


The Lexar Professional Line will outperform Sandisk the higher you go in class as well.

But, for photographers, and every day enthusiasts.

Stick with something middle of the road like the Sandisk 32GB Extreme SDXC UHS-1 card I linked above and here.

Stefan Glazer the Professional Amateur
Stefan Glazer the Professional Amateur

Photographer, Artist, Pug Dad, Podcast Host, Teacher, Friend

Articles: 162

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