If you are running around where you live in a city or large town...
Go to
www.streetmap.co.uk
Enter name of street where you start
Print out map of route
With piece of string, mark out distance of route (start at one end of the piece of string, bend around the corners etc, cut it when the route ends)
Measure string against the OS grid on the streetmap (at most detailed size, one grid is 500meters, so two grid lengths = kilometer)
Much more accurate and cheaper than pedometers and crap, and has the added bonus of being a skill you will need to know once in the forces.
