Understanding SD flash memory card speeds
SD (secure digital) cards are becoming increasingly popular for digital camera storage. They’re tiny, convenient, and getting affordable in sizes as large as 1GB and 2GB. But they come in a bewildering array of different speeds and prices, even within one manufacturer’s line. What’s with the different card speeds, and which one do you need for your camera? This article gives you the details.
Understanding SD Card Speeds
While the first SD cards were very similar between brands, each brand now offers cards in several different speeds for each capacity. To make things more confusing, SD card speeds are measured in two different ways: in kilobytes or megabytes per second (KB/s or MB/s) and in an “x” rating similar to that of CD-ROMS. The “x” is the minimum CD-ROM speed of 150KB/s, so here’s a table of equivalent speeds:
- 4x: 600 KB/s
- 16x: 2.4 MB/s
- 40x: 6.0 MB/s
- 66x: 10MB/s
- 133x: 20MB/s
Understanding available options
While this varies between manufacturers, most offer two or three categories of speed. At this writing, here’s a summary of what each category means:
- Basic SD cards (Sandisk, Lexar, etc.) are the cheapest models. They generally have a speed of 1x to 16x, but often don’t guarantee a particular speed, so you won’t find anything about speed listed on the package.
- “Pro” SD cards (Sandisk Ultra, Lexar High Speed, etc.) list a speed of 32X or higher. Some have speeds up to 66x (10Mbps).
- High-end SD cards (Sandisk Extreme, Lexar Professional, etc.) have a speed of at least 66x. The latest models (i.e. Sandisk Extreme III) have a speed of 133x.
Since these categories are vague, and not always meaningful—for example, Sandisk’s “Ultra II” and “Extreme” cards are the same speed, but “Extreme III” is a higher speed—you should always compare based on the actual speed listed on the package. If it isn’t listed, assume you’re looking at one of the slowest cards.
Which one do you need?
Which speed you need depends on your camera. While even the fastest cameras can make do with a slow SD card, they’ll be at their best with a card that keeps up with the camera. Here are some general rules for choosing a card:
- If your camera is a consumer point-and-shoot model ($400 or less) chances are it works fine with any SD card. Some of the newest models can benefit from a 66x card for burst (multiple picture) or movie modes.
- If your camera is a “prosumer” model or a digial SLR ($400 to $3000) choose the fastest card you can get for a good price, a 66x card if at all possible. These cameras are fast, and a fast card will improve their response time.
Note that I haven’t recommended 133x cards for any camera. The SD card specification (version 1.0) is limited to 66x, so the 133x cards work in a “double speed” mode available in version 1.1 of the specification. At this writing, no cameras take advantage of the full speed of these cards, but you may want to consider one anyway—there’s a good chance you’ll still have the card when you upgrade to the next camera.
Conclusion
If you want the final word on which card to choose, check your camera’s manual or specification for speed requirements. Note that “burst” or movie modes may require higher speeds than still photo modes. Another tip: find a review of your camera at a site like DPReview.com, which does timing tests on cameras to determine their speed with different cards.
Another thing to consider is getting pictures from your camera to your computer. If you have a fast card and a fast card reader, you’ll enjoy the faster transfer speeds even if your camera doesn’t need them. Most USB 2.0 card readers (available for $10 to $20) can handle very high speeds. In fact, this is the one area where the 133x cards actually live up to their promise.
One more tip: definitely choose one of the good name-brand cards over the cheaper generics. With potentially 500 or more photos at stake, you don’t want to take chances. Sandisk, Lexar, Viking, Verbatim, and Crucial are good brands.
An excellent article!
Comment by Tony P — August 15, 2007 @ 12:40 pm
Perfect – Exactly what I needed… I bought the 10mbps Card (x66) for AU$85 for my new Canon G9. But needed some info on the SD Cards.. Thought I might need the x133 card but huge price difference..!! So looks like I have made the right choice…!! Thanks Again for the info.. Riles
Comment by Riley J — November 6, 2007 @ 7:19 pm
How does that compare to the new SDHC cards?
At first glance it looks like many of the old SD cards are faster than the fastest new SDHC cards. Class 6 is the fastest I know of and quotes a speed of 6 MB/sec????
Are the old cards really faster than the new ones?
Comment by Ana Mouse — December 3, 2007 @ 12:43 pm
The class of the new SDHC cards only refers to the write speed of the card – not the read speed. So a class 6 card will allow data to be written to the card at a minimum of 6MB/s but it may read data from the card at 20MB/s. The older (non SDHC) cards never specified a write speed, only a read speed.
Comment by Glen — January 2, 2008 @ 9:00 am
I have a bunch of SD cards at home, and today was the first time I realized that they all operate at different speeds. A year ago, I bought two Kodak 1GB SD cards for just $20. I thought, “Wow, what a bargain!” Today I did some testing and found out that these Kodak ones have a transfer rate of 3.2 MB/s. No wonder they were a bargain! They work fine in my digital camera, but they are awful to use in my Pocket PC. I install Pocket PC programs on these SD cards, and if the card is too slow, the program will crash. Luckily I have a faster 9.8 MB/s card I can use.
I wish I knew about speed when I was buying SD cards. I thought only size mattered. Well, now I know.
Comment by Johnny — January 16, 2008 @ 3:53 pm
What causes SD cards to fail (magnets and crushing damage aside)?
Comment by johnnyallenshaw — February 5, 2008 @ 8:15 am
Thanks for the information, very useful indeed. I wanted to comment on you suggestion to possibly buy a faster card that only a future camera might make able to take advantage of. With prices falling like big rocks, it doesn’t make sense to invest in more capacity / speed than you need currently.
Comment by Corey — March 27, 2008 @ 2:49 pm
The brand “Kingston” was not mentioned. I have always been very happy with this brand for both flash-cards and laptop memory. One company mentioned in the authors list offers a free computer scanner (to assess how much memory ones computer can accept). The misinformation produced by that scanner has made me “go off” the brand. Ripping ones laptop apart looking for the mythical second slot is a great waste of time.
Comment by Davey — March 29, 2008 @ 4:01 pm
I appreciate the article and its logical explanation of info. I have looked on the DPReview.com site, but can not locate where they test cameras with different speed cards. I am interested in the Canon Xti and also the Panasonic tz3 as I am purchasing the newer versions of these as they become available. THe tz5 takes HD video, so I’d like more card speed info… THanks! pdean11@hotmail.com
Comment by P Dean — March 31, 2008 @ 6:33 am
Thanks for the helpful article. For P. Dean; the DPReview.com site posts camera performance with storage cards with each review they do, usually under that camera’s review link for Performance or Timings and Sizes. They will tell you which card they used, and then the performance while using that card for various file sizes.
Comment by Dennis — April 5, 2008 @ 8:07 am
Thank you for your very, very useful article!
Comment by Mihai — April 22, 2008 @ 2:06 am
Just bought a Canon G9 & your article was a great guide to the SD world.
Comment by Ken Mick — July 11, 2008 @ 9:34 am
Really good info.
Comment by Angela — October 19, 2008 @ 1:49 pm
I don’t understand any of this, I hate the big cards(600 photos), When I want to load the last few (say 6) I’ve just taken, it takes ages to go through them all and how do I avoid the ones I don’t want?
Comment by Lena — September 23, 2009 @ 1:04 pm
I have just bought a new Canon camera with a card but wanted a spare SDHC card. With a plethora of makes, versions and speeds out there your article proved very useful for me buying spare cards. The article explains simply and clearly, even to me as a lay person, card speeds and which would be appropriate for my camera.
Thanks Andy
Comment by Andy MacTaggart — April 9, 2010 @ 4:58 pm