Roughly how long will my package take to arrive from the UK to Australia?

Okay, so.
It's supposed to be a backpack I ordered, so it's not very heavy and will probably come in a small-ish box/package. It's coming via air mail, but roughly how long will it take? I ordered it two days ago.

it will arrive about 2 weeks after it is posted.

• Tristan, when your ordered it, and when it is shipped are two different animals, The postal services, will always inform you to allow 15 working days maximum, not including day received from the shipper.
  You should be asking the shipper, you know the people you ordered the thing from, not us.