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How to Pick the Right SD Card

Once you buy a new camera and lens, the only thing you absolutely need is a memory card. As a result, choosing one of these cards is a subject all of us need to face at some point. It is sort of confusing because there are many different numbers on the face of these cards. What we will do in this article is help you pick the best one.

Comparison of 64GB SD memory cards

Most cameras these days use SD cards (SD stands for Secure Digital). Even cameras that use larger Compact Flash cards now often support SD cards as well. In this article I’m going to focus on SD cards, although much of the information will translate over to CF cards as well.

Before getting into the meat of this subject, I have gone through the SD cards on the market and made a chart that lists them by size. For each size of SD card, I list them by brand and then by price. The idea was to clearly see the deviations between cards based on brand and speed. A lot of what I’m about to write comes from the data in that chart, so if you are interested in seeing the underlying data, click on the button below to download it.

SD Card Comparison

A Quick Tour of the SD Card

There are many sizes, speeds, and brands to choose from when selecting an SD card. In addition, there are various ratings and other numbers that appear on the card. It all seems designed to confuse you. The reality is, however, that there are only 2 numbers that matter. You just need to decide on the size and the maximum speed of your card. Here is where you will find that information on the face of the card for the two largest brands of card:


While those are the two numbers on the card that really matter, as you can see there is a lot of other information on these cards. What is all that stuff? Most of it is outdated and not particularly relevant to you, but here’s what this information is telling you:

  • Speed Class Rating: In the graphic above, the rating that is the 10 with the circle around it is a minimum read/write speed rating. It is an older rating that doesn’t tell you much. If the card is verified to always write above 10 MB/seconds, it is a Class 10 card (as in the example above). If the card always writes at least 4 MB/second, it is a class 4 card (and so on). Pretty much all cards read and write at least 10 MB/second these days, so they are all 10’s. In fact, if you look at the chart I created of the cards on the market, every one of them is a Class 10. So there is no point spending much time on this rating.
  • UHS Speed Class Rating: In the graphic above, the rating that is the 3 that looks like it is in a bucket relates to a minimum sustained write speed. If the card has a minimum write speed of at least 10 MB a second, it rates a 1. If it has a minimum write speed of at least 30 MB per second, it rates a 3. It is mostly important for video and most cards are 3’s anyway. There actually is some variation among cards here, but this is adequately addressed by just looking at the maximum speed rating.

There is one useful aspect of these class rations though, which is that they pertain to write speeds, whereas the MB/second figure I pointed you to above relates only to read speeds. In most cases, the read speed will give you a good indication of the write speed as well. The write speed will be slightly slower, of course, but usually not by too much. There are occasions, however, where the write speed will be significantly lower than the read speed, and these class ratings can be useful in making sure that a card with a high read rate also writes as fast.

There is one other number that appears on Lexar cards to address. Lexar cards feature prominently a different speed rating that is something like “1000x.” This is another rating that can be safely ignored. It is based on the read speed of audio CDs at 150 KB/s. If you wanted, you could use this to figure out the speed of the card in megabytes per second, but why bother when it is printed on the front of the card already?

Does the Brand of SD Card Really Matter?

Almost everyone recommends you stick with the “good quality memory cards.” By that they mean to stick with SanDisk and Lexar. In a sense, that is obvious. A card failure would really, really suck. However, I am dubious about whether those who insist you buy certain brands actually know which SD cards actually have a lower or higher failure rates. I have never seen the failure rates of the manufacturers compared, and I spent quite a bit of time searching for this information in writing this article. I suppose it is a difficult thing to compare, so there might not be any data.

As a result, I do not know if there are true quality differences or if they are all coming off the same assembly line and getting different stickers (and prices). Honestly, I have used off-brand cards in the past and never had a problem.

Having said that, would I recommend that you do the same? Probably not. As card prices have continued to fall, it is now the case that you will not save that much money by going off-brand. Again, check out the chart listing the available SD cards by size. If price is an issue, you would save a lot more by getting cards that write slower than you would by changing brands.

So, therefore, I will be just like everyone else and advise that you be safe and stick with a brand you know. Please understand that this piece of advice is not because I know which brands are better than the other, but just that the cost difference isn’t that great.

What About Speed?

The speed of the card will limit the camera’s ability to write to the card, and also the ability of the computer to read from the card. Some allow this to occur faster than others. As we saw in the graphic above, the speed is set forth in megabytes per second on the face of the card. The speed of a card is something you should consider because the same sized memory cards can vary pretty dramatically in price depending on speed.

How much does speed matter to you? That depends on what sort of photography you do, of course, but unless you are holding down your shutter button in continuous mode for a long time, it is not likely to be a problem you face.

The reason for that is the camera has a buffer. The buffer is memory in the camera itself that holds image information when you take pictures until the pictures are written to the memory card. Unless you fill up that buffer by taking many pictures in a row, the time the camera spends writing to the memory card will never come into play. The size of buffers varies by camera, but newer and better cameras tend to have larger ones. In any case, the point is that unless you are shooting more than a few pictures at a time, the speed of the card will not matter to you at all.

Some photographers blast away continuously at a high rate of speed in an attempt to catch the perfect shot. Sports and wildlife photographers come to mind. If you are one of them, then get a fast card. Otherwise, there is really no need for fast cards. I wouldn’t get the slowest cards, but there is no point in spending to get the fastest cards as the price difference is significant.

If you are really concerned with the speed of memory cards, check out this website: Camera Memory Speed. It reviews memory cards and also tests them in different cameras. Choose your camera and it will tell you the fastest cards for your particular model, and will do by measuring the “average write speed” instead of the maximum burst. (Thanks to Bill Ward for pointing me to this website and also for helping me fix a mistake in a prior version of this article).

Do Memory Cards Wear Out?

With traditional computer storage, the question has never been whether your drive will fail but when it would fail. They have moving parts and will eventually crash and burn. Memory cards, on the other hand, don’t have that problem. But do they wear out?

It seems that there are limits to the use of SD cards, but these limits are not likely to be a problem you face. Here’s why:

  • Time: There is no stated time limitation for SD cards. The SD Association (who knew there was such a thing?) says that an SD card will have a lifespan of 10 years or more. By sticking the words “or more” to the end, that shows me that they really have no real idea. The odds of you using the same card for 10 years are very slight (more on that in a minute).
  • Reformatting: There is a limitation to the number of times a memory card can be reformatted, but it shouldn’t matter to you. The limit is over 100,000 times.

Therefore, it does not appear that having your card wear out is something you need to worry about.

Further, the most likely outcome for your card is not that it wears out, but that it becomes obsolete. As file sizes and card sizes continue to increase, older cards are eventually no longer big enough. (You have probably experienced this if you have been photographing for many years, and are probably are wondering what to do with all your cards measured in megabytes.) At some point it just isn’t worth using these small cards anymore.

What Causes Memory Cards to Fail?

The most common cause of failure to memory cards is actually physical damage. People seem to worry most about corruptions or internal errors, but if you avoid damage to your card the odds are failure are quite small.

If you do have a memory card failure that is not due to physical damage, the failure is likely to happen immediately. Therefore, it is probably a good idea to take some throwaway pictures and format your card a few times to make sure it works properly. If you get through that with no problems, the odds of you having a problem with your card (while already quite small) go down even further.

Finally, if you do have a memory card failure, there are a few reasons why that will probably happen. The first is an error of your camera in writing to the card. There are a few things you can do to reduce the odds of this happening:

  • Use the camera controls to format the card after you have downloaded pictures onto the computer. Do not use the “erase all” function.
  • Do not take the card out of the camera until the camera is completely shut down.
  • Don’t run your batteries all the way to failure as it could lead to a write error.

If you follow these suggestions, your odds of card failure are very, very small. I have actually never had a card fail on me. It does happen though, but it is uncommon.

What Size SD Card Should You Get?

There are those that caution against getting one large card because it is like putting all your eggs in one basket. Corruption of a card with a huge amount of pictures on it would be catastrophic. Rather, they encourage you to buy several smaller cards and switch them out periodically. That way if one card fails you do not lose all your pictures.

I actually disagree with this philosophy. My primary reasons are:

  • This advice presupposes that you are going to walk around with thousands of pictures on your card at any one time. That may be true for a wedding photographer, but not most others. The reality is that you are probably going to load the pictures onto your computer after each day of shooting, and that probably won’t be more than a few gigabytes of pictures. Even though you have a large card that will hold a lot of pictures (which is nice for those rare occasions when you do need a lot of storage), that doesn’t necessarily mean that you will have that many pictures on your camera at any one time. Usually you won’t.
  • In any case, it seems to me the largest danger your card faces is being lost or damaged outside the camera. The card is pretty safe inside the camera. Even if you were foolish enough to bang your camera around (and we all know you wouldn’t do that), the card is safe and sound inside. These cards are small items that are in much more danger of being lost, damaged, stolen, etc. outside the camera. In addition, if you a juggling several SD cards you might get confused and inadvertantly delete a card you want or shoot over the data. Is this likely? No. But it is many times more likely than card corruption.

That said, I wouldn’t buy the largest cards available because they generally charge a premium for them. Something like a 64 GB card is plenty big, won’t cost that much, and will hold a few thousand pictures.

Ok, Smart Guy, Pick One.

So which one should you buy? There are too many variables for me to pick one for you.

Therefore, I’ll just answer for myself. If I was buying a card right now, after having looked at all the data, I think I would buy the Lexar Professional 64 GB card that costs $34.40 with a max speed of 95 MB per second. Why? Here are the reasons:

  • Size: A 64 GB card is plenty big, and will hold over 2000 Raw files at any one time.
  • Speed: While I am not that concerned about speed, this card is fast, with a maximum speed of 95 MB per second (and pretty high minimums as well, judging from the ratings).
  • Brand: It is Lexar, one of the top, most-reliable brands.
  • Cost: Very reasonable cost. This model is priced well under what the comparable San Disk model costs. It actually isn’t much more than the comparable off-brand models.

I really don’t need a card that big or that fast, but for under $35, why not?

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