I brought my fitbit on my PNT hike this year, and spent a little time this weekend getting summary data. My hiking partner Lucky and I hiked 804 miles in 53 days, of which 5 days we did no hiking (so 48 hiking days), for a per-day average of 16.8 miles.
In those 48 days I walked just a bit over two million steps, and we climbed the equivalent of a little over 25 vertical miles along the way.
What I found interesting is how much fitbit's daily mileage estimate was high. I expected it to be high; I used a level track at a local school to establish my average stride length, and unless you're road walking on pretty level roads, real trail involves on average shorter steps. But for the PNT this came out to be 30% high, and if I did some more work to remove Nero's, and even more to remove known road walking miles, for actual trail it would be higher than that. Perhaps 30% would be more reasonable for better quality and better graded trail like the PCT.
FWIW, I have the fitbit "one", which I kept in a key pocket at my hip; I personally can't stand to wear a fitness tracker on my wrist all the time (I guess I'm in the minority on that one, at least based on what's being sold today).
If you're into geeky hiking stats, a little more information on this is here:http://www.postholer.com/journal/Pacific-Northwest-Trail/2016/brianle/2016-10-24/Some-Stats/57530