How to Select the Right Camera Memory Card


In today’s market if you want to buy a camera memory card, you may find it challenging to select the right one. A card comes with the following criteria; type, speed, price, capacity. If you want to buy a high capacity card with low price it might come with a low transfer speed. If you wish to buy a high transfer speed with high capacity card it may come with a really high price. If you want to strike a balance between both, you really have to compromise on quality.

Paul Hudson

By Paul Hudson

What is a memory card?

A small removable memory medium which can be used to store data on one medium and to transfer the data to another medium.

Let’s see each criteria which will help you decide on a memory card in detail.


This one is fairly straightforward, and not a big deal. A 32GB memory card can hold up to about 1000 RAW photographs. Assuming that one RAW file size is 30MB, in general a Canon 5D MKIII will produce a RAW file between 25-35MB in size. Likewise a 16GB card can hold up to about 500 photographs, and so on. If you shoot in jpeg format, then a 32GB card can hold around 3200 photographs, assuming you have your jpeg settings as fine in detail, and large in file size. With that setting a jpeg file will come in at an average size of 10MB on a Canon 5D MK III camera.


There are many types of memory cards available on the market ranging from Micro SD card, SD card, CF card, M2 (from sony). But there are only three type of cards being used primarily in the photography world, Secure Digital (SD) card, Eye-fi card, Compact Flash (CF) card.

Micro SD card

Micro SD card is a miniature version of the SD card and meant to be used in mobile phones. This card has capacity, as well as transfer speed restrictions. That is why it is used primarily in Smartphones where one can store music and apps, or any other relatively less active data.

Daniel Sancho

By Daniel Sancho

Secure Digital card (SD card)

This type of the card is widely being used in digital cameras, primarily in point and shoot cameras and secondarily being used in professional cameras. The constraint in using this card is the capacity of the card. The initial high capacity is only 2GB when introduced in 1999. But as the time and technology progressed a later version as SDHC is introduced with a higher capacity of 64GB in 2006 (HC means Higher capacity). The recent third iteration of SD card been announced in 2009 as SDXC cards (XC stands for extended capacity). This type of card offers up to 2TB and increased transfer speed.

Eye-fi card

These are unique SD cards that come with built-in WiFi. This allows you to transfer the data to your computer or a cloud based service or even to your Smartphone directly, thus enabling you to clear off the memory as you shoot, without having a need to replace the memory card. It is even possible to geotag your photographs with the available wireless service, but with less accuracy though.


By bfishadow

There seems to be a promising future for this card!

Compact Flash card (CF card)

First introduced in 1994, CD cards have high speed, and high capacity. This is the reason why CF cards occupy the primary card slot in professional cameras. Present SD cards are equalling the speed and capacity of CF cards, but camera manufacturers are not leaving CF cards just yet. They often provide slots for both an SD and CF card, but some photographers wish they would offer two SD card slots instead. This provides some extra space inside the camera and saves money for the photographer (CF cards costs roughly twice that of SD cards). Hopefully they will switch the importance to SD cards in the near future.

As the name suggests this is a flash memory which aids high speed reading/writing speed, and has a higher capacity too.


Speed in SD cards

All memory cards come with speed, either mentioned or not. Speed here means both writing and reading. The one indicated on the card is the maximum speed the card can read, but the most important thing is the write speed. Read speed is the time taken to read the data from the card and the write speed is the time taken to write the data. Simply put read speed comes into action when you transfer the data from the card, write speed comes into play when you shoot. In general the write speed is about half of the speed of read speed in SDHC cards. In few other cards both the read and write speeds are about the same.

Simon Yeo

By Simon Yeo

The speed of cards have been classified into classes by the SD Association, which are referred to below. The speeds are primarily meant for video recording, where sustained recording (write) is required and it is supposed to be the minimum worst case scenario speed.

You really need to give weight to this one single-most important factor, when you buy a memory card. All SD cards have a class noted on them. Check the attached diagram below:

Class Minimum Speed
2 2MB/s
4 4MB/s
6 6MB/s
8 8MB/s
10 10MB/s

Later, in 2009 another class, UHS, was introduced by the SD association and is designed for SDHC and SDXC memory cards. UHS utilizes a new data bus that will not work in non-UHS host devices. If you use a UHS memory card in a non-UHS host, it will default to the standard data bus and use the “Speed Class” rating instead of the “UHS Speed Class” rating. UHS memory cards have a full higher potential of recording real-time broadcasts, capturing large size HD videos and extremely high quality professional HD.

Courtesy – SanDisk website.

UHS Class Minimum Speed
1 10MB/s
3 30MB/s

Speed in CF cards

When it comes to CF cards the speed is often mentioned as X times and in many cards it’s been mentioned as MB per second, which is pretty straight forward. Whereas when the speed is mentioned as 600X or 1066X what exactly does it means? X means 150Kb per second. It is a standard brought over from optical media recording. Now to find out what exactly the speed is of 600X – to find this multiply 600 by 150 and divide the result by 1000. The final result is in MB per second. Eg., a 600X speed card is capable of 90MB per second read speed (600?150/1000).

The latest CF cards come with the UDMA 7 which improves in clearing the camera’s buffer memory quickly, which allows the camera to get ready for the next burst. Firmware upgrade is required for the Canon 5D MKIII (yours may require it also, check with the manufacturer) camera to make full use of UDMA 7.


When it comes to price, the fastest card is the primary criteria which decides the price. The next deciding factor is capacity of the card. An SD card is 50% of the price in the same capacity CF card. So, if you want to buy a high speed card with same capacity you will need to pay more. On the other side if you want to buy a high capacity card at a lower price, it is possible to do so but you’ll get a lower speed card.


  • If you use two cards at different speeds, the lowest speed is the deciding criteria for the burst. For instance if you use a CF card at 90 MB/sec in one slot and an SD card having the capacity of 45MB/sec (and you set RAW files for both cards) then you won’t get the advantage of 90MB/sec and the possibility of missing the shot. You have to use both cards at the same speed.
  • If you do not upgrade to the latest firmware for the 5D MKIII camera, the host memory will perform for UDMA 6 which significantly consumes more time in clearing the buffer memory.
  • I wish the camera manufacturers would switch to SD cards completely for both slots. The speeds of the SD card already matches with the CF cards, there is no point paying twice the price, and we’d get the added bonus of saving space inside the camera.
  • In few cases the SD card speed is higher than CF cards. For instance SanDisk Extreme Pro speed is 280 MB/sec but from the same manufacturer the CF card’s maximum speed is 160 MB/sec.

Hope you have gotten a bit of information from this article. Do share your thoughts in the comments.

Read more from our Cameras & Equipment category

Navan Viswa is from India residing in Chennai now. He does weddings, products, industrial projects and travel photography. He studied as a Civil Engineer and worked as one for 12 years, found that the job not of interest and his passion was aligned towards photography. So he quit his job and is now roaming with his camera for commissioned and non-commissioned works. You can see more of his writings on his blog and more photographs on his web page as well as 500px.

  • heat_fan1

    Micro SD cards actually have the same speed ratings as SD cards, up to UHS-3. Because of their versatility, they have become my favorite cards to use. I can use them my phone, tablet, GoPro, and, with the adapter, any device that accepts an SD card. And the cost increase over SD cards is very low.

  • Keith R. Starkey

    I didn’t see any UHS rating on any of the images of the cards. Is this rating stated on the card, stated sometimes, or not stated at all? Thanks.

  • Navaneethan

    Oh is it? Thanks for the info. But the speed is one thing we need to consider before buying micro SD cards.

  • Navaneethan

    Keith – It’s been stated in all the new cards coming to market nowadays. Cheers.

  • heat_fan1

    Here’s an SD card that’s UHS-3:

    Here’s a micro SD that’s also UHS-3:

    You can also get micro SDs up to 128GB, though SDs up to 256GB are available. You might want to revise your article a bit. The fastest and largest-capacity SD cards are faster and larger than micro SD, but that’s at a level that is much greater than anyone needs. Micro SDs are useful for much more than just phones (especially considering that GoPro and other action cameras can only accept them).

  • Keith R. Starkey

    It’s been stated “in” or “on”? since I didn’t see it on the card, how would I know if it’s a UHS 1 or 3? Thanks.

  • LesCarter

    So, when shooting, the bottleneck is invariably the write speed of the card?

  • Navaneethan

    Yes Les, it’s the only thing which could affect the burst shoot.

  • Navaneethan

    It’s on – typo. If it is not mentioned on the card, the only option is to look into the specs.

  • Dandan

    I think my micro sd extreme, which i bought 2 years ago, writes 38meg/ second. MicroSD extemepro 64gig does 98meg/second. they’re built for 4K raw vids.

  • Navaneethan

    Thanks heat for letting us know. I am convinced somehow that the Micro SD cards can be used in DSLRs with the help of adaptor, but a photographer who shoot actions like sports photographer cannot use them anyway. Because the SD card speed comes at 280 MB/per sec which would easily serve the purpose of the photographer who shoots 10 fps (RAW).

  • ash

    Cfast cards are replacing cf cards

  • jwi

    What about the writing speed of the camera itself ? There’s a hardware limit too, isn’t it ?

  • You missed a few things. For one thing another reason many pros prefer CF is the durability. They fail much less frequently than other formats. On the other hand in my own real-world testing the built-in SD slot on my MBP and iMac offer far faster transfer speeds than any USB adapter I’ve tested not to mention one less device to lug around and that sometimes makes me lean towards my SDs when transfer speed or mobility are a priority. What I usually do though is shoot raw to CF and JPEG to an SD, which is sometimes an eye-fi. I don’t use eye-fi the way you talk about here though – I tether it to my iPad which I can hand to my client so they can observe my work as I’m shooting – for which the JPEGs are fine.

  • Also – something I discovered on location in Nepal… the eye-fi KILLS the battery life on your camera, so don’t use it if charging your camera batteries are going to be an issue (it was there).

  • heat_fan1

    When shooting continuous, there are two factors to consider: shooting rate and the maximum number of shots. The camera had its own internal memory, so the rate is fixed and driven by the camera’s capability. Nikon’s D750, for example, can shoot at 6.5fps. The number of shots you can take continuously is impacted by the camera’s ability to quickly transfer files to the cars. Therefore, it’s impacted by both the size of the buffer in the camera and the write adopted of the card. The D750 can shoot up to 10 continuous shots without delay (just under 2 seconds), if the card is of an adequate speed.
    In general, any Class 10 or UHS-1 card is plenty for just about any camera that accepts SD cards.

  • heat_fan1

    That’s all true, but you’re referring to a small group of special photographers. It’s true that shooting continuous for several seconds with a 30 MP camera or 4K video might not work as well with a micro SD, but for most camera users, micro SD offers fast more flexibility for a marginal cost increase.

  • Navaneethan

    Agree with you Sander about the battery part when using Eye-fi card. May be this one single most issue could restrict the growth of that card in the market.!

  • Navanee Viswa

    Yeah, I understand. But I guess the camera manufacturers are not falling behind the memory card manufacturers. A detailed insight might required to discuss about this further.


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  • Angie

    I have a slightly off topic question…
    Which CD type do you recommend for burning images to. I’m always lost when I look at all the options but they all seems to work.

  • Rick Johnson

    I get up to 14 shots shooting 14-bit NEF RAW shooting to Samsung Pro 64GB UHS-1 cards. Those write at a max of 50MB/sec. A SanDisk Extreme Pro UHS-I is available that can write at 90MB/sec. I imagine those would flush the buffer a bit more quickly. That said, a UHS-I card much above that speed would be pointless in most cameras, including the D750.

    Why? The camera’s SD controller plays a big part in write speeds. Very few UHS-II capable cameras exist today outside of 4K video recorders, so those 280MB/sec cards would be a waste if the camera’s card slot didn’t have the extra pins required for UHS-II compatibility. At that point, you’d max out the UHS-1 bus at about 104MB/sec (+/-) vs 312MB/sec max for UHS-II.

  • SD Cards will show either the old speed classes or the UHS, not both. All the pictures of SD cards above are using the slower system which is a circle around a number. The faster UHS cards show the number inside a U.
    The only SD cards I’ve seen that didn’t show the speed on the card or packaging were cheap knockoffs that should be avoided anyway. Pay the extra for legit name brand cards, SanDisk always works well for me. More info on wikipedia including the speed symbols:

  • JB

    I have an older DSLR (Canon 1Dmk3) that cannot take advantage of the faster cards, BUT, it still helps when downloading to PC so I am not waiting for as long.

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  • Matthew Signorini

    Love that shot of core memory 🙂 It’s from before my time, but I learnt about it in programming classes. Crashing programs still generate core dumps (on Linux at least), despite the fact that memory technology has moved on.

  • mike winslow

    Do this article as a chart and it might be useful. Did you mention about how cards may be formatted differently, and it’s always best to let the camera – writing device – format the card?
    , Some cameras use both SD and SDXC. Others require SDXC. Some camera video formats such as AVCHD will record up to a half hour of data at 28 Mbps ( under 4 mBytes/sec), but stored on the card as multiple 2Gb files due to the file system. A vendor reader might take the fragments and re-assemble them into a single contiguous file on a notebook. Lightroom will not do this in all cases.
    Speed becomes interesting typically in capturing bursts of stills in RAW format, since the class 10 handles video codecs up to ~80Mbps.. A burst of x 30Mb raws in one second – 10 fps, 24Mb file=240 mbyte = 2 billion bits.. So a card which writes 100Mbps can do twice as many bursts as one which writes 50Mbps.. See how interesting that stuff is?

    Things like memory sticks or CF or the little micro sd cards. That’s sort of like the square peg, round hole thing which most people can figure out.. What they typically need help figuring out is why two cards which look the same dont work.

    Which cards are backward compatible – eg there is overlap in size in which two formats?

    SD cards have a maximum size before they must be SD__ ?? Help the poor reader out. Dont make them struggle.

    Think chart.. people like charts..
    How to buy:

    Does your memory card look like: A,B,C or D.

    There is usually a symbol on the memory card slot. Can you find it, does it look like one of these? :

    Maybe you cant find the symbol, but different memory cards started appearing in different years. We know with pretty good certainty that a camera made 10 years ago isnt going to work with a 256 Gb card.. Hey – there’s another useful chart: year/max Gb and also year/ (cost/Gb)..

    Also, some people dont know a good deal over a bad one, so they might wand some advice on what is a good price today. Of course – that count also be done on the graph, but historical price ranges would be difficult to do without allot of work and have dubious accuracy anyway, so just stick with an at the time of printing range..

    At the time of printing – another bugaboo – technical publications should always have a date. Like this article – when was it first posted?

    And the eye-fi.. ugh.. I’d point out that a multi-function WiFi/memory card is helping you to add WiFi to a camera that doesnt have it. It’s going to be more expensive, have a different and complex setup, and generally not the best choice when memory is the only consideration.. They do serve a purpose. They will make you even more eager to get a camera with built in Wifi, after trying to use one of these bridge devices..

  • Mark

    Yep, I’d certainly rate CF cards as being able to take significantly more punishment than flimsy SD cards. I do like the lock feature on SD cards though.

  • Well I think that the eye-fi has a limited lifespan as a product anyway as more and more cameras are including these features directly in their cameras. Before long we won’t remember NOT having GPS/Wifi/cloud options being a part of our cameras.

  • I have never used the lock feature on my SD cards. Never even crossed my mind, though I knew it was there.

  • My main point was that I have a solid collection of all 3 and use each of them for different reasons and in different situations.

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  • Phil Coxon

    That’s a really simple one to answer. Buy a write once CD (i.e. a CD-R and not a CD-RW), but better still use a DVD as the capacity is higher. As for manufacturers, there really is only one quality manufacturer left, and that’s Verbatim, preferably the AZO coated ones, but not essential.

    Once you’ve recorded them, stuck them in a jewel case, put them away somewhere safe, and they’ll still be there in 50 years time.

  • Pio Danilo Cuadra

    In terms of reliability, I have never been a fan of SD cards. I rely on Lexar and Transcend 128GB and 64GB UDMA 7 cards. How much more, especially now that CFast CF cards are circulating in the market. No professional photographer using professional SLR models in his right mind , will entrust himself to SD cards. the price of a fast CF may discourage many, but surely there is no such thing as ” free lunch” ..Remember that.

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  • Phil Coxon

    Absolutely right. I work for Verbatim and we have noticed no measurable drop in speed between a MicroSD with adaptors and a full size SD.

  • Phil Coxon
  • Phil Coxon

    I agree with almost everything you say with just one exception. Cameras are backwards compatible with older, lower spec cards. You can’t use an SDXC in a camera that was designed for SD, but you can use SD in the latest cameras (with the accompanying low speeds).

  • alex comaya

    my opinion is that if your camera uses SD card, you will not buy micro SD if your shooting professionally. why? SD cards are intact while micro SD has moving parts / contact point inside its adapter. if you plan to use it with other gadget like mobile phones or goPro then switching to SD holder adapter frequently, you will damage the micro SD contact soon and chances are your micros SD will get corrupted and we don’t want that to happen if we are paid to shoot. if for personal use only, maybe, but professionally, don’t take chances and buy SD card for SD slot of DSLR.

  • Alex Vidal

    Also good to know what cards your camera can use best. For example, the T5i can only use up to UHS1 due to the buffer. Purchasing a UHS3 would be a waste of money.

  • heat_fan1

    That’s all fair for professionals. Since most of the readers of this blog are not professionals, they may find value in using a small number of cards between several devices. I know i do.

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