I also find that the 1/2 hour per mile and 1/2 hour per 1000 feet works for me. To simplify the math, I'll divide the total distance by 2 and add 1/1000th of the elevation. For example, a 8.6 mile hike with a 2400 foot elevation change will take 8.6/2 + 2.4 = 6.7 hours. My actual times are...