Whenever I run on the roads I'm able to figure out exactly how far I ran. When I run on trails I'm usually on my local equestrian center trail system. It's a bunch of intertwined trails. Somehow I always end up on one that I've never been on before.

My question is: When you run on trails do you try to figure out your mileage or do you just go for time? If you try to estimate mileage, how do you do it? I know that I'm running slower on the trails than the road because I'm trying not to kill myself on rocks, loose sand, etc. but I have no idea how much slower I am.