Bits, bytes, kilobytes, megabytes, gigabytes, terabytes - what's the difference?

Published: 25th January 2010
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What's the difference in the various types of file sizes and how does this affect your internet download quota? Let's first take a closer look at file sizes.


Short for binary digit, a bit is the smallest unit used in computing. Nowadays, you'd be pretty hard pressed to find a file size in just bits.


Made up of 8 bits, a byte usually represents one character of data. For example, the sentence "how now brown cow" would be 17 bytes in size (spaces also count).

Kilobyte, KB, kB, K or Kbyte

A kilobyte is 1000 bytes. You'll see kilobytes used to describe file sizes for things like low resolution photos and small text-heavy Word documents (like a resume).

Megabyte, MB or meg

A megabyte is a thousand times bigger than a kilobyte. If we do the maths, 1 MB works out to be 1 million bytes. In every day terms, a typical MP3 file is usually around 3MB in size. A high resolution photo will be about 2MB, while attaching a ten slide PowerPoint presentation (with words and pictures) to an email will be about 1MB.

Gigabyte, GB or gig

At 1 billion bytes (1000 MB), a gig is... well, pretty big. One gigabyte is about 16hours of your favourite MP3 music files. It's about one iTunes movie download or three hours of watching TV over the Internet. When it comes to web browsing, a gig lets you surf about 500 regular websites (and yep, just looking at a page means you're downloading).

Terabyte or TB

A terabyte works out to be one trillion bytes or 1,000 gigs. Most computer memory and hard drives on the market are measured in gigabytes but we're steadily seeing more and more super-sized terabyte options on the scene.
How do I know how big a file is?

If you're running a Windows operating system, it's easy to check the size of a given file. You'll need to right-click your selected file (in My Computer or Explorer), select 'Properties' and bingo - you'll see a window showing file size info. Alternatively, try holding the 'Alt' button while double clicking the file with your mouse.

If you're working on a Mac OS, hit the 'Control' key while clicking on the file in Finder. Next, select 'Get Info' from the menu that pops up - easy.

How do I manage my monthly internet download quota allowance?

You can make the most of your monthly download quota (and avoid being shaped) by making sure you're on the right high speed internet plan to suit your usage habits.

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