If you're not sure how many kms your regular route is, you can check at http://www.gmap-pedometer.com/
The site is really great, you just click and drag the map to move it around to australia (unless you wanna check distances in america), then zoom in using the buttons on the left of the map until you get to around your streets. Then you can hit "start recording" on the left, and double click to mark your starting point. double click again at any "bends" in the road, and it will measure the route for you! you can go around and make a whole route, and print the map, or you can go a certain distance then tell it to come back. you can make it do miles or km.
I think its really useful.