Don't forget to consider the condition of the trail. A perpetually wet trail, or a poorly maintained trail is a more difficult walk than a dry dirt road. Vertical rise is the elevation change during the hike. If you start at 1,500 feet elevation at the trailhead and top out at 3,000 feet on a mountain summit, your vertical change is 1,500 feet, though you may have traveled several miles. Also, trails are not always a steady incline, but descend some during the hike, before climbing again.
Milages below are round-trip.
Level - 1 to 3 miles . Accessible by nearly everyone. One to two hours. Up to 500 feet vertical - 1 to 3 miles . Especially young families.