In reply to TheDrunkenBakers:
All my running is on trails and mostly in the French Alps so I use tracedetrail.fr. It allows you to draw the route over an IGN map and then generates profile and distance. You can print out a road book with the map to take with you.
There might be an equivalent in the UK (although I think you can use it for UK routes) but I find stuff like Strava route planner too difficult when away from major roads and trails as it likes to snap to well known paths.