Note that for Qantas domestic Jet Flights you are permitted 1 x 115cm (45") bag or 2 x 105cm (41") bags.
Internationally it's 1 x 115cm (45") + a personal item.
Also not that for a laptop computer to be considered a personal item it must be carried in a "slim bag". Laptops carried in "large laptop bags" will be counted as part of your carry-on baggage allowance