If you are really that keen to know how far you have run try this link to google pedometer.You can trace in your route and it will tell you the distance and calories burned. Not very good,memory map is much better.Both have the fault that they only show distance in 2 dimensions,if you do a fell run with 5000ft of climb and back to the start,there are nearly 2 miles of ascent/descent to add on.

Probably best to just ask someone with a fancy GPS wrist watch. Link