I just got back from a long run comprising both road and muddy footpaths. I'm trying to increase my endurance/milage and was wondering if it is possible to 'convert' off road miles into an estimate of road miles?

And while we're at it. Where's the line between trails/footpaths and X-country? Never really figured that one out.

If you are wearing spikes then you are running cross.
See the trail running association website for the definitions.

I know spikes is best for cross but... I'm not wearing spikes and focus mainly on roads but that doesn't keep me from taking an occasional run on footpaths (which around here is nothing but edges of fields) with mud flying around my ears. Just wondering if that would be classified as cross.

XC is short and all off road usually......
Trails is a mix of all sorts

I only really class a run as XC if it's a race classed as XC.

If I'm on a training run that goes across fields and stuff then I just call it an off road training run. I'd class a trail run as a run away from roads but on established paths.

To be honest I don't think there is any real distinction between any off them.

XC races also tend to be more club runner based event. You see very few people competing at an XC without a club vest on.