The battery on my Garmin ran out before I finished my little OHT hike, but Tim Ernst's guidebook puts the distance at not quite 25 miles. I'm going with that because he's wheeled the entire trail twice. The Garmin samples position periodically rather than continuously causing smoothing of switchbacks and such, short-changing my mileage by several percent. No problem. It took me about eight and a half hours. Nice hike!