@Mike Robinson Just use the in-car navigation system! It's very accurate and the only case where you will have a difference in real mileage is in strong winds.
In any case, all superchargers are always shown on the map if you set it in "map" instead of "satellite" view. You will also notice that some of them are bright red, and some others are light red. The difference is that the brights ones are those reachable from your current position with your actual SoC (State of Charge), the light red ones are the un-reachable.
On top of that, the route calculation in-car is dynamic, meaning that it recalculates the route every few minutes based on the state of your charge and the traffic ahead. If for whatever reason it thinks the indicated supercharger is too far to reach, it will recalculate the route to another supercharger, or suggest a slower speed just to be on the safe side.
Be confident, it works!