Running out of hard drive space is no fun. You're either left running to Officeworks to get yet another external hard drive to dump things on to, or you are forced to make the tough decision of what to delete.

Thanks to a free tool called WinDirStat (Windows) or Disk Inventory X (Mac), it's now easy to find out what files you should move or delete to free up the most space.

These tools analyse what is on your hard drives and then show them as a bunch of squares on a page. The colours represent what type of files they are, and the size shows how much space it is taking up.

What on earth is that big green square taking up all your space? Simply click on it to find out! You can even right-click on it and choose to open that location on your computer, allowing you make further decisions from there.

So stop scratching your head wondering what on earth keeps chewing up your disk space! Download one of these great free tools and find out the answer.