File size: a tutorial

To many people, file size is a black art.  Worse, for many, file size just does not feature on their radar at all.

File size is how big a piece of digital information/ a digital asset is, i.e. how much storage, memory and bandwidth it consumes.  File size impacts on performance: the bigger something is, typically the slower it will be to open, be it a Word document, a large picture or similar.  File size is an issue when putting things on the web, as the bigger a file is, the longer it takes to download for the end user.  Equally, it can impact on email in a big way.

To many people, file size is a black art.

Some broadband providers put a limit on the amount of data the you can download per month: obviously file size relates to that.  Especially if you are using a mobile phone: some providers use per KB billing, so the bigger the file, the more you pay!

Units of size:

The basic unit of file size is the kilobyte (KB).  This is 1024 bytes, each of which is madeup of 8 bits and represents a single character.

You'll often see files expressed in terms of kilobytes and for larger files, megabytes.  A megabyte (MB) is 1024 kilobytes.  Nowadays, the specs for computers are quoted in terms of Gigabytes, which are 1000 megabytes, or a million kilobytes.

So below, we've put together a ready reckoner of typical file sizes for various digital assets.

The File Size Ready Reckoner *

file typecommentsfile size
.txt1 page of plain text4KB
.doc1 formatted page, no images29KB
.xlsTypical 1 page spreadsheet18KB
.mp3typical 5 minute song6MB
.wmv1 minute movie for youtube (low quality)2.5MB
.htmltypical web page50KB
.jpg1500x900 pixels - i.e. 5"x3"800KB
.jpg200x300 pixels - typical for the web15KB

* all quoted file sizes are approximate.

Other Typical examples

An album of mp3s - 100MB
A 2 hour feature film - 600MB


See also: