How much less distance do you travel if driving around Australia counter clockwise versus clockwise? We drive on the left.

This person has calculated the difference as 19m in a distance of 15,000km to circumnavigate Australia

One source had it at 14,000 km, which is about what you get when you add up the distances between each of the major cities. One fellow decided to go around Australia on a Caterpillar Grader, and travelled 15,000 km ...

Is it quicker to drive around Australia clockwise or anticlockwise?

The short answer is anti-clockwise, as we drive on the left of the road. The extra few metres isn't going to make much difference, though when travelling in the anti-clockwise direction you will get the benefit of the Fremantle doctor when crossing the Nullabor. You can work out the difference mathematically: take an average distance between the lanes (3 metres) and the total road distance around Australia, turned that into a circle, and then work out the difference in circumference between the bigger and smaller circles. One suggestion is that it should be 2pi X (separation of the lanes) so say 3m between the lane centres - that's about 19m. It may not be that simple ..

http://www.thetravelalmanac.com/australia/around/trivia.htm

That calculation would be mathematically correct if the roads didn't have zigs and zags. This means that sometimes the clockwise trip is on the inside of the bend, rather than the outside. The net effect of that is going to be that the difference is even less in practice than in the idealised situation. An exact answer would require calculations from maps about the relative stretches of the road that bend in the same direction as the (general) coastline, and what percentage are actually curved in the opposite direction. Then there are the stretches over which the road is dead straight (such as crossing the Nullarbor), and the length is the same in both directions. So it actually will depend on the exact roads you choose!

https://www.mapsofworld.com/australia/road-map.html

For the curious amongst us (me included), the calculator on this website confirms the 19m calc by the travelalamanc.com is correct, lol

a radius of 2387324.1m gives a circumference of 15,000,00m -- and a radius of 2387321.1m (the 3m difference by driving on the other side of the road) gives a circumference of 14,999,981m.

https://www.omnicalculator.com/math/circumference