Sending a parcel to Australia means you will be using the Royal Mail not Australia Post although Australia Post will look after it at this end. The Royal Mail has a parcel post rates calculator here:
http://www.royalmail.com/parcel-despatch...
Ask at your local post office,you are using Royal Mail,not Australia Post.
You need to take the parcel to the Post Office. It has to be weighed and you have to do a customs declaration form for any parcels going to Australia.
You need to take it to any post office. They will weigh it and sell you the correct postage as well as supplying the customs form that needs to be attached to the envelope
It wil depend on the weight too, the Australia Post site would be a better place to check
5 Pounds.
Ask the Post Office
What? You can find your way to Thailand and Vietnam, but you can't find your way to the post office?
What a moron