It does actually give you the exact mileage for a run (I don't have a Garmin or similar device), but this site allows you to map the run wherever you run, not just on roads; you can go across fields, and golf courses, down paths and trails and round parks. It also has a great nutrition section and it tells you how many calories you can have a day and works out how many calories you've burned according to your activity. It also maps all sorts of other activity, including lawn-mowing etc! It also builds up a database of your distances, times, time per kilometre etc and graphs it all. The ads are a bit annoying, but are easily ignored. A great site which I'm sure does all sorts of other technical stuff - I've probably only scratched the surface - but very useful.