Why Hard Drives and Memory Cards Have Less Space Than Advertised

Have you ever wondered why computers always indicate that your hard drive or memory card has a smaller storage capacity than what’s advertised on the box (and the card itself)? No, it’s not because you got a defective card, it’s not because your card came preloaded with a bunch of unwanted files (your hard drives, maybe), and it’s not because the manufacturers are cheating you by skimping out on the storage space (well, not directly, at least). The reason has to do with math and marketing.

Humans think about numbers in base 10, the decimal numeral system, because we have 10 fingers and 10 toes. That’s why the parts of numbers are called “digits” — just like the parts of our hands and feet.

Computers, on the other hand, think in base 2, the binary numeral system.

Herein lies the root of the issue. The “brilliant” marketing gurus at data storage companies decided early on that all their products should be marketed in the decimal system, since that’s what consumers understand.

Therefore, one megabyte on their products is equal to 1,000,000 bytes, and one gigabyte is equal to 1,000,000,000 bytes. To a computer, however, a megabyte is 1,048,576 bytes and a gigabyte is 1,073,741,824 bytes.

Thus, for each gigabyte advertised in base 10, you’re actually receiving about 70 megabytes less than a gigabyte in base 2.

Take a close look at the box your hard drive or memory card came in, and you’ll notice asterisks. Look for the fine print, and you’ll see a disclaimer stating that the figures are stated in base 10:

Memory cards aren’t as bad as hard drives when it comes to advertised versus “actual” (it seems that the makers try to match up the two figures): when you buy a card for your camera, you’ll probably getting something close to what it says on the box.

Buy a large external hard drive, however, and you’ll likely see a much bigger difference between what the box tells you and what your computer reports.

(via Lifehacker and About)

  • slvrscoobie

    if your worried about .08gb out of 32Gb you need to take a chill pill.
    This information has been around for YEARS and is less important every day. Every HDD has had this same issue. The bigger issue is format type (NTFS, MacOS..) and how much overhead they waste.

  • Michael Zhang

    Never said we were concerned about the .08. Just sharing this fact with readers who may have never learned it before. :)

  • Sebastien Prune

    Yes, 1024 vs. 1000 conversion of Mega, Giga… is not the only problem. Formating the drive also takes place on it, moreover if you use a lot of small files : you need more “inodes”. As someone said, it all depend on the FS (fat, ntfs, zfs, hsfs, ext3 and so on…)

  • Arnold Newman

    Good refresher on this issue.

  • guiie

    Hard drives don’t come with less space than advertised. They advertise GB and Windows uses GiB to calculate space. It is a “grammar” error at most if you want to argue. Mac OS X shows GB instead of GiB since Snow Leopard. Given the fact that someone took the job of writing this article, the title shouldn’t have less effort in the making.

  • Gonzo

    Sector Size makes a bigger difference in how much data the drive or card can ultimtely hold anyway. If you have 8k sectors and you’re storing a bunch of 1k files, you’re wasting a lot of free space because every one of those 1k files takes up 8k of disc space. That’s an over-simplification but you get the idea, yes?

  • Xavier Michelon

    In addition to this marketing trick there are other factors worth mentioning.

    1) Once you have formatted your card, you are also losing space because of the filesystem overhead: in order to keep a list of the files and folders on your storage devices, some space on the drive is reserved to store ‘an index’ of the content (the file allocation table or FAT, and there are generally more than one copy of this FAT for safety).

    2) Bad clusters. Any storage device will after some time have portions of it that does not work anymore. The filesystem can detect these problems and mark those portion as ‘bad’, subtracting their size from the available space.

    3) Cluster size alignment. Files are stored in clusters of fixed size. This size depends on the total amount of storage. Typical cluster sizes are 32kB, 64kB, 128kB, … A cluster can only contain data for a single file. so in the case you have a cluster size of 64kB, and you want to store a 65kB size, you need 2 clusters, and you are wasting 63kB in the second one. Of course, in the present context as we are dealing with files of several MB, losing a few kB here and there is not really a problem.

  • Raymond Andrews

    You shared the least significant and most widely known fact while completely neglecting a much more relative and significant “fact”

  • Steven Alan

    wow, chill people.

  • Leon

    On the contrary, most companies don’t manufacture different capacity hard drives. They make them the same size and then limit the capacity through software. You can go to computer forums and see how you can unlock the “locked” space of your hard drive.

  • Raymond Andrews

    Beware of the zombies roaming the street, they may trample your flower garden …. instead of THEY WANT TO EAT YOUR BRAINS :)

  • Dmitry Munda

    Captain Obvious’s topic :)

  • Michael Zhang
  • JB

    A 2×4 is not 2×4.

  • Happy_Tinfoil_Cat

    It didn’t used to be this way. Years ago, hard drive manufacturers used the base2 numbering. I’m sure some marketing ‘genius’ thought that it would be a good idea to short-change his customers and round up using base10. In that highly competitive market, other drive manufacturers would feel they needed to do the same to stay competitive. Nowadays the edge they gained makes little difference and customers are doomed to always being confused. Add in the loss of capacity due to OS partitioning and formatting and it is messy to the lay person. The only ding I have against me in eBay is from someone who just couldn’t comprehend that the formatted capacity of the CF showed up smaller in his camera. He feels I cheated him by swapping a 483MB card for a 512MB and switching the labels.

  • lai

    The Ebay bit is hilarious.

  • Bob T

    Care to elaborate? My Google skills are failing me; I can’t find any mention of unlocking the “locked” space of my hard drive.

  • Jared Monkman

    which fact is that

  • Mansgame

    They could just round down. I’m kidding.

  • micksh

    Seagate got sued for that and lost. This was 5 years ago.
    According to that settlement they now have to include disclaimer – how they define Gigabyte.

  • Ivan

    I am in the IT business since mid 80s and I still remember storage media being advertised as X KB/MB/GB of “unformatted capacity”. The term “unformatted” has disappeared about the time we stopped worrying about where to place jumpers for master/slave HDD mode or how to correctly enter tracks and cylinders in BIOS configuration (younger readers are likely unfamiliar with those operations). So the catch is in “unformatted” vs. “formatted” capacity. Since “formatted” capacity depends on the file system used the only fair way is to specify “unformatted” capacity, and that’s what all manufacturers are still doing, but usually without mentioning it. After formatting available space gets reduced, and it has been like that since the dawn of storage media, thus nothing new.

    BTW, part about base2 vs. base10 (which has nothing to do with “reduced” capacity) reminded me of a good joke — What is the difference between a novice and a seasoned programmer? Novice believes kilobyte has 1000 bytes. Seasoned believes kilometer has 1024 meters!

  • Felipe_Paredes

    Michael, do you get stress reading this comment? you must be a very patient block.

  • the Trouble


    Should talk about GiB rather than GB and MiB rather than MB if “listener is a human”.

    In a computer world 2 base (binary) and 16 base (hexadecimal), both, are much better then 10 base (decimal) and that is the basic reason for this conclusion…

  • Michael Zhang

    Haha. I guess I take a lot of chill pills regularly :)

  • RandomRudy

    Your screenshot is bad. 32 GB is 29.8 GiB, not 31.91 GiB. Mac OS actually displays GB, everything is correct here. The missing 0.09 GB got lost somewhere else, not in the calculations between GB and GiB …you should have used windows to show the described problem :)

  • jerry sawyer

    This is incredibly informative! I really felt this thing when I purchase my new memory card for may phone just recently. But is this not fraud or something?

  • david

    isn’t this just flat out false advertising???? I mean whats so complicated about writing down on the box exactly how many gigabytes there are??? you don’t need to bring in any math at all… for example if I have a terrabyte hard drive I should have 1000 gigs, but instead I only have 800 or so… I could simply write on the hard drive 800 gigs. why cant the companies just do this and save me the hassle???

  • david

    LAWSUIT!!!!!! lol

  • Luka Error

    My 32gb external only has 29.7 in reality. It is irritating.

  • Dalton

    The memory of my computer was advertised as 500, but it only has 455

  • Pete Harper

    “Humans think about numbers in base 10, the decimal numeral system, because we have 10 fingers and 10 toes.”

    That’s not completely true – I’m sure I saw a doco once that showed an ancient civilization that had a numbering system based on 5s, so it would be “1, 2, 3, 4, 10, 11, 12, 13, 14, 20″ based on 5 fingers and 5 toes.

  • Nico

    Not so funny when you buy a 3TB HDD and it has 300GB less than advertised. 300GB is a lot of space, they should stop using 1GB =1000MB and use the real 1024 instead.

  • FraggleExposer

    Sorry mate. But you, sir, are a prize twat.

  • NagatoYuki Huntress

    Ok all of tjis is mumbo Jumbo technical jargon that most of us do not care about the fact is that the companies that make storage mediums such as internal and external hard drives and solid state devices like memory cards and CD/DVD/Blu Ray and whatever else that comes down teh pike in the years to come should be honest and make sure that out of box the product comes as it is advertised. These companies can made devices with the extra capacity so when i plug that device in to my laptop or computer and it is formatted ( today external drives are all ready and plug and play and already formatted ) that I should see exactly what i paid for . I buy a device that says 3 Tb’s I should see when i plug that device in 3 TB usable not 2.75. I find it funny that the bigger the hard drive the more they take out . so a 4 TB hard drive i assume has 3.5 tbs free . come on whatever process it needs for formatting should not be a exponential thing. We know these companies can build products that compensate for the formatting issue and make sure we get a product with the usable space advertised and stop using mumbo jumbo terms to get away with basically being thieves. If i own a restaurant and say i am serving you a boneless 16 oz Prime rib . you bet i am sure your going to get that 16 oz prime rib. i am not going to cut off 2 ozs and tell you oh we actually take off 2 ozs cause of and give some restaurant lingo mumbo jumbo. you get what you expect . Likewise companies that make products should make sure their consumers get a product that has the amount of usable space expected . don’t swindle your customers. Its called fair business practices. They don’t want to be cheated out of usable product they buy nor should their customers be swindled. if they want to swindle us . I would like to have their names and city they live so we can make sure when we see them getting products from grocery stores and such we give them less than they where paying for and see how they react. Oh sorry sir i see you work for sea gate we have to take 10 percent of your purchased items out of their container we cant give you the full product you pay for.

  • Alexander

    the problem for me is with a 2tb hard drive I am missing 48 GB of space and with 4 TB 96 GB of space I can do a lot with that space

  • Deofelzan Ryan Solis

    what if you only got 14.6GB instead of 16GB… can i press the panic button now? :)