Ask LH: Why Doesn’t My New Hard Drive Show The Right Amount Of Space?

Ask LH: Why Doesn’t My New Hard Drive Show The Right Amount Of Space?

Dear Lifehacker, I just bought a new 1TB external drive, but my computer is only showing that it has 902GB on it! What’s the deal? Am I getting scammed out of 100GB? Sincerely, Greedy for Gigabytes

Dear Greedy,

Your hard drive may be reporting a smaller number for a few reasons, but the first thing you should know is that you probably aren’t being “scammed” out of data — that number is completely normal. Here’s why.

External Drives Often Come With Software Installed


The first (but less important) explanation is that many external drives come with backup software from the manufacturer. Generally, we recommend getting rid of it, as it’s rarely better than the stuff you can download online (such as our favourite backup program Crashplan). So while it probably won’t free up heaps of space, you should probably format that drive before you do anything else.

If you’re a Windows user, just right-click on the drive in Windows Explorer and choose “Format”. Format it to NTFS if you’re planning on storing a lot of data (like music or a backup), and FAT32 or ExFAT if you plan on using it to transport files between Macs and Windows PCs.

If you’re a Mac user, go to /Applications/Utilities/Disk Utility and click on the drive in the left sidebar. Click the “Erase” tab in the middle pane, then choose your file system from the dropdown. Mac OS Extended (Journaled) is the best default option for storing a lot of data, but FAT32 and ExFAT are better if you’re using it on both Mac and Windows.

Once you’ve formatted it, you won’t have those annoying software popups when you plug it in, and you should have a bit of extra free space on the drive.

Hard Drives Are Measured One Way, Marketed Another Way


Here’s the bigger reason you have less space: computers are based on binary maths, which means storage is counted using base 2 — not base 10, which is what you see on the box. So a kilobyte is actually 1024 bytes, not 1000, which is what it says on the box. Similarly, a megabyte is 1024 kilobytes, a gigabyte is 1024 megabytes and so on. That means the actual amount of space on the drive is going to be lower than what it’s marketed as, with the difference being bigger as you get to bigger drives. In general, for each gigabyte reported on the box, you’ll have about 70MB less space, which means that your 1TB drive has closer to 900GB.

There isn’t much you can do about this, unfortunately. If you’re a Mac or Linux user, you should update your software, since more recent versions of OS X (10.6 and up) and Ubuntu (10.10 and up) actually use base 10 to report storage space and file sizes, which should make it easier for you to judge (that’s also why if you move a file from a Windows machine to a Mac the file will appear bigger even though it isn’t — it’s being measured with base 10). Unfortunately, there’s no way to “fix” the problem in Windows — you just need to know that you’ll get a little less space than what you see on the box and act accordingly. If you have 1000GB of data, a 1TB drive won’t be enough, and you’ll want to buy a 1.5TB instead. It doesn’t matter whether it’s internal, external, or even a thumb drive — this affects every kind of drive out there.

Cheers, Lifehacker

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  • Really? So “Truth in Advertising” doesn’t cover using international standards of measure (megabytes-Mb, gigabytes-Gb and terabytes-Tb) and we can be misled like that? When they say megabyte, they mean 1 million bytes, rather than an actual megabyte. I feel sure that the Trade Practices Act in Australia might have something to say about that. Or am I misreading what you’re saying here?

    • Thing is, the international standard *is* 1 million bytes, as defined by the IEC. It’s just that a number of software companies have historically used the (incorrect) 1024^2 definition. At one point, the IEC published a new standard defining kibibytes (KiB), mebibytes (MiB), gibibytes (GiB) etc (the “bi” being short for binary) to try to make things more clear by having a separate term for the binary-based definitions, but software companies have been slow to adopt them.

      Take a look at

    • To be fair, I’m pretty sure all HDDs have to be labelled with a disclaimer stating “1GB = 1,000,000,000 bytes” or something like that, although it’s typically in tiny print on some obscure part of the box.

      Still, is it really that hard for companies to use base 2 format on their packaging? Anyone computer literate enough to purchase their own hard drive likely already knows the original “gigabyte” is equal to 1,024 megabytes and so on.

  • “fix the problem with windows”??? how about we just force everyone to stick to base 2, when this has been the standard since drives were first made..?

      • Actually, technically it is a problem with windows. According to the standards, a megabyte is actually 1000000 bytes, which is what they are marketing it as. If you want to say something is 1024*1024 bytes, that’s called a mebibyte. So, Microsoft should either label their free space as 920 gibibytes or write 1000 gigabytes if they want to be correct (which is what Apple started doing with Snow Leopard).

  • Surely marketing this way should be considered illegal and deceptive, but when I tried to make a claim againse Maxtor for their shoddy underhand practices, the ACCC had no idea what I mean by base 2 and base 10, so it became troublesome to take things any further…

    • The manufacturers aren’t really wrong here though, if they say 1TB they mean 1 terrabyte which is defined as 1,000,000,000,000 or 10^12 bytes, whereas most computers will list 1TB when they really mean 1 TiB or tebibyte which is 1,099,511,627,776 or 2^40.

      Really, Windows should either be writing GiB/TiB instead of GB/TB or convert over to using base 10, otherwise they’re the ones not being compliant.

  • “That means the actual amount of space on the drive is going to be lower than what it’s marketed as.”

    “In general, for each gigabyte reported on the box, you’ll have about 70MB less space, which means that your 1TB drive has closer to 900GB.”

    The actual capacity of a drive doesn’t change across operating systems, only the method of measurement. I remember plugging in one of my old 500GB portable drives into a Mac, it showed up as a 500GB drive. In Windows, it shows up as 465GB. The space is still there, it’s just Windows measures differently using binary multiples. There is only a very, very slight loss of actual space – due to the file system the drive is formatted to.

  • Also worth noting that the filesystem itself takes up space on the drive. On a large drive with a journalling filesystem, this can make a noticeable difference (not 100GB worth, but still).

  • On the bottom of an HP drive box, “As used for storage capacity, one megabyte (MB) = one million bytes, one gigabyte (GB) = one billion(…)Total accessible capacity varies depending on operating environment.” I think mebi-, gibi- and tebibytes would have been worth mentioning in the article.

  • Most drive boxes state the fact that

    a) Actual formatted capacity may be less
    b) One gigabyte = 1 billion bytes

    From the bottom of my Seagate GoFlex box:

    “When referring to drive capactiy, one gigabyte, or GB, equals one billion bytes[…]. Your computer’s operating system may use a different standard of measurement and report a lower capacity. In addition some of the listed capacity is used for formatting and other functions.”

    Therefore it isn’t false advertising, and as the comments above state, Windows is incorrectly reporting drive space, not OS X or Linux.

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