| Distance | 100 miles (~161 km) |
| Status | Benchmark ultra achievement |
| Run through | One or two nights |
| Needs | Training, fueling, crew/pacers, resilience |
A 100-miler is a 100-mile (about 161 km) ultramarathon, widely regarded as a benchmark achievement in trail and mountain running. Run over rugged terrain and through one or two nights, finishing one demands months of training, dialed-in fueling and hydration, crew and pacer support, and deep mental resilience. Famous examples include Western States and the UTMB.
The big one
The classic goal of ultrarunning, run with a crew and pacers while chasing the cutoffs.
Frequently asked questions
What is a 100-miler?
A 100-miler is an ultramarathon covering 100 miles (about 161 kilometers), usually on trails and in the mountains. It's considered a major milestone in ultrarunning, requiring runners to keep moving for the better part of a day and through the night, managing fueling, pacing, sleep deprivation, and terrain over an immense distance.
How long does it take to run 100 miles?
It varies enormously with the course and runner: elite athletes finish mountainous 100-milers in roughly 14–20 hours, while most finishers take somewhere between 24 and 30+ hours, often right up to the race's cutoff. Flatter, less technical courses are faster; rugged mountain courses with lots of vert are much slower.
How do you train for a 100-miler?
Training builds a deep aerobic base over months with high weekly mileage and vert, long back-to-back runs to accustom the body to fatigue, terrain-specific and night-running practice, and rehearsed fueling and gear strategies. Most runners also progress through shorter ultras (50K, 50-mile, 100K) first and arrange crew and pacers for the event.
Sources
- 100-mile racing — American Trail Running Association
- Ultra endurance — The Mountaineers