The "classic" Inca Trail (there are variations) is 26 miles (45 km) long. Most traditional treks take four days and three nights, with arrival at Machu Picchu early on the fourth day.
Elevations range from about 8,000 feet to a high point of just under 14,000 feet at Warmiwañusqa (Dead Woman's Pass). The route also ascends to and descends from two other slightly lower passes. Much of the trek is on ancient stone paths, some of which are extremely steep.
Our trek, with Enigma Peru, followed this format...however, we walked farther than other groups on day one and day two, thereby having the first two nights' campsites all (or almost all) to our ourselves.