I wasn't sure that this would be possible but it is now since they have added a measuring tool. To measure a distance you need to right click on any point on the map and select "measure distance". Then click on another point on the map to make a path and you will see the distance measured between those two points calculated in either miles or kilometers.
If you want to remove what you have done you just tap "undo" and to clear all points just choose More in the top right hand corner and then clear. Google maps has become such a handy tool now with so many features that I think sat navs will eventually take second place. Having tried both I much prefer google maps for navigation.