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Why Is My 32GB Flash Drive Actually 29.8 GB?

Monday, May 7th, 2012 by | Filed Under: File & Disk Management, Hardware & Peripherals

Dennis from MD writes:

I recently purchased a 32GB USB Flash Drive. Using Windows 7’s computer button to view all system connections, I selected the new drive and requested its properties via a right-click.

It indicated a capacity of 32,027,770,880 Bytes followed with 29.8GB.
Why is there a difference between these numbers, and actually how much available space is on the drive?

USB Flash Drives, along with hard drives and other types of computer storage, are measured in bytes. The problem is that the definition of a megabyte/gigabyte isn’t really the same between computers and storage manufactures. A computer says a kilobyte is 1024 bytes and a megabyte is 1024 kilobytes. So one megabyte (one million bytes) is actually 1,048,576 bytes. To get to 32 gigabytes you have to multiply 1024 (bytes) x 1024 (kilobytes) x 1024 (megabytes) x 32 (gigabytes) which gives you 34,359,738,268 bytes of information.


However, computer hard drive and storage makers had the clever idea that a gigabyte is defined as a “billion” bytes, so why do they need to give you extra bytes you didn’t pay for just because someone who made the PC decided 1024 bytes are in a kilobyte? So industry practice is to label things in even numbers, even though computers will see less space as measured in GB. You do get 32,000,000,000 bytes when you buy 32GB, but your PC isn’t counting the same way everyone else would!


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8 Responses to “Why Is My 32GB Flash Drive Actually 29.8 GB?”

  1. Eric Peterson says:

    Thank you for explaining that, while I am very tech savvy,this is the first time I’ve actually seen it explained this way. And while I personally think it’s a bunch of BS what the storage manufacturers are doing, I alone cannot make them change their systems. I’d prefer if every hard-drive, flash-drive, cd, dvd, blu-ray or whatever would actually list the true size of the device once it has been formatted for the computer. I don’t mean to say sell a 32gb flash-drive as 29.8gb. I mean just have somewhere on the label the actual size after formatting. That way, when someone make a purchase, they know exactly how much free space they will have. At least then, they will know when buying a 1tb hard-drive that they will only get approximately 976gb and not the full terabyte>

    • bobbintb says:

      technically, it is not the drive manufactures in the wrong. the prefix -kilo means 1000. in reality it is the pc vendors you are using the incorrect terminology. now the drive manufacturers may have done this as a marketing gimmick back in the day or there may have been just an honest disconnect. i dont know. there is a slow movement to start using the proper terms, and i believe even the latest mac os correct defines a gigabyte as 1000 kilobytes.

  2. DJL says:

    Formatted capacity is ALWAYS less than the rated sizes. It has more to do with the way the computer actually works rather than the manufacturers trying to cheat us.

    This is where you really get into it. It’s about parity, and bits and bytes and word size and how much space it takes to store that comma or character in the memory spot. There’s SO much more going on that takes some considerable depth but it really has nothing to do with the manufacturers not complying with the 1024 kilobyte size or anything like that.

    Blame the folks who invented the file system and file structures. 1 kb is still 1024 bits no matter how you look at it.

    There are spaces accounted for bad sections of the hard drive/flash drive that the file creators don’t give you access to.

    There’s space used up by the file system to ‘index’ the amount of space. All those things gobble up the 1024 bits that make up a Kb…leaving you with much less space than you thought you should have.

    Absolutely nothing to do with the manufactures quibbling about what makes up a bit and a byte.



  3. Ron says:

    Your explanation correct, but very simplified.

    For those more detail oriented, the difference is how the 2 groups count. As you say, the disk manufacturers took the cheaper way out. They use “normal” “base 10″ or “decimal” counting. On the other hand computers have 2 states, on or off, so they “count” using “base 2″ or “Binary”. This difference is also the reason for strange results where say 3+2 does NOT equal 5 (but in much larger numbers or smaller). Decimal numbers are converted to an from binary, causing rounding errors.

    Back at the start of computing, the difference wasn’t significant, but now that anyone can buy multiple terabytes at home for US$100-200 the diffence is getting more troublesome. On a TB drive, the difference is 93GB. The next increment is Petabytes, there is 117,253 GB difference or 115 TB!

    PS: you answered this question back in 2004 (but the page is gone):

  4. OptimalSupreme says:

    Wrong, ITs the way that x86 sees it. Amiga a true Unix system, and sees ,more then what is available or sees all the available space, and a 32 gig thumb-drive I can have 35 gigs. Its just an excuse for a redefinition of how crappy x86 architecture is .Plus how old and arcane it is.

  5. RubixCub3 says:

    Why would 2 of the exact same USB sticks (Kingston 32GB) and the only difference being the series number, show up with 2 separate values? both plugged into the same computer (front side USB hub) one shows as 29.3GB while the other shows as 28.8GB. Does this have something to do with the USB hub taking away 500MB?

    • Josh says:

      Part of the reason that they show up different sizes has to do with redundancy. When you make billions and billions of little tiny transistors, not all of them are going to work. Like any industry there will be a defect rate. The system is designed to compensate for defects, both factory defects and failures over time, so that your files are not corrupted. Bad cells are marked as bad and not used. So two drives of exact same theoretical capacity will have varying actual capacity, and that capacity may change somewhat with time. Also different operating systems may give you more or less usable space based on how much space is required for redundancy of data and how much is required for file structure itself (telling the computer which memory cells hold which files).

  6. Petal says:

    I have an 32GB flash drive which is encrypted by MacAfee. I do not have much data stored on it but it keeps telling me that I have no free space. When I first noticed this, I deleted a bunch of stuff but it still says no free space. How do I fix this so I can add more stuff to my memory stick

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