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How to tell if you are buying the correct SD card

Secure Digital (SD) cards are used in all types of devices, from computers to video cameras to mobile phones, which means you'll probably have to buy some. But how do you know if you're buying the right one? There are tons of options out there, and they are difficult to distinguish, but the noticeable difference in price indicates that something makes them distinct. How can you know if you are getting the right one for your device? Here are four things you need to check before making a purchase.

Cut it

There are three different sizes of SD cards: standard, micro and mini . The standard SD card you're probably familiar with. Its size of 32 x 24 mm small, but actually the largest SD card size available. Most computers, cameras and camcorders use these dimensions. Many microcontrollers and single-board computers (such as the Raspberry Pi and Arduino with an adapter) also use this size.

The medium size option, at 21, 5 x 20 mm, the miniSD. This dimension is much less common, although it is used in some phones. Many miniSD cards include an adapter that allows them to be used in standard sized SD card slots, like this one from SANOXY:

Much more common than miniSD, however, microSD. These cards are tiny, at 11 x 15 mm, which makes them perfect for mobile phones and tablets. As with miniSD cards, it is easy to find adapters that will allow you to use microSD cards in standard size slots, like the adapter supplied with this Transcend 64 GB microSD card:

The size of the card you use depends entirely on your device. If you have a standard SD card slot, you will need to use a standard SD card or a smaller one with an adapter. If it has a miniSD slot, you will need a mini or micro with adapter. And if it has a microSD slot, you can only use microSD cards.

Type of paper

There are three different formats of SD cards : SD, SDHC and SDXC . For the most part, their labels are related to capacity. SD cards can hold up to 2 GB, SDHC cards up to 32 GB and SDXC cards can hold more than 32 GB . Almost all devices and card readers can read SD and SDHC cards, but if you want to use a card that can store more than 32 GB of data, you need to consult the device's user manual to make sure it is compatible with SDXC – card format (this is becoming increasingly common).

The label of each card indicates the size of the card with one of the following logos:


If you've looked at the legions of SD cards available, you've probably noticed that there is a wide range of capabilities available. The first SD cards were available in 32 and 64 MB capacities, but the smallest SD card that most people will consider today contains 2 GB. And while there may be bigger ones out there, few people will be interested in an SD card with a capacity of over 512 GB (these monsters are available from PNY).

Obviously, almost certainly not necessary to spend $ 350 to get 512 GB of storage space. Instead, you'll need to think about what you'll be using for the SD card. For example, if you want to use a microSD card to hold more music on your phone, 16 GB will be enough. Depending on the quality of the music, it will probably be possible to add somewhere between 2,000 and 3,000 songs to that card.

Even an 8 GB card will hold over 2,000 compressed photos, making it a safe choice for phones, tablets and cameras with which you plan to take pictures. If you are using a DSLR, the file size will be larger, so you will have room for less photos. This is especially true if you save images in RAW format, which can be up to 25 MB per or more per image. If you take many RAW photos, you may need an even larger card, such as 16 or 32 GB.

Storing video on an SD card requires even more space. According to SanDisk, about four hours of standard HD video can be stored on a 16 GB card. Less than three hours of high quality HD video would fit on the same card.

These estimates come from some hypotheses, but can be used as a guide to help you understand if you are buying the correct SD memory card. Fortunately, many SD card manufacturers will give you an idea of ??how much information you can put on a card, either on the SD card package or on the manufacturer's website.

Speed ??class

One of the lesser known parts of the SD card's nomenclature is the speed class, which indicates the speed at which data is written to the card. Fortunately, this SD Association table makes it very clear:

If you don't use the SD card to record videos, you don't need to worry about the speed class; writing data from a computer or a camera does not necessarily have to be at very high speeds (although it certainly doesn't hurt to have a faster card). If you're using your card to record videos, though, you should check this table to make sure the card you're using is fast enough for the type of recording you want to do.

For example, if you're filming in HD, you should have a Class 6 or faster card, and Class 10 would be better, especially if you're about to take HD photos even during video. If you are recording in 4K, a UHS 3 card will be required. The speed class of each card is displayed directly on the card. Just refer to the chart on the card and look at the table above.


One of the most useful features you may be surprised to find is that SD cards can include wifi connectivity. While this idea was made popular by the Eye-Fi SD card, but a number of other brands, including Toshiba and Transcend, now also offer connected options. When using an SD card connected to the wifi network in the camera, you can transfer photos wirelessly to your computer or smartphone.

While this is not an essential feature, it can be very beautiful, especially if you tend to accidentally forget the SD card in your computer or card reader. Obviously, you will pay more than you would for a card not enabled for the wifi network. A 32GB Eye-Fi card costs $ 76, or $ 100 for one that comes with some professional level features, like automatic photo grading.

Choose the right card for you

If you understand these four SD card qualities, you should have no trouble finding the right card for your needs, whether it's storing additional documents from your computer or recording 4K videos. By observing the size required by the device, determining the capacity you need, understanding the difference between speed classes and thinking about wifi connectivity, you will limit your seemingly endless choices for an SD card to a much more reasonable selection.