Quick Answer
A 50km (31 miles) is the shortest common ultramarathon. The main standard distances are 50km, 50 miles (80.5km), 100km (62 miles), and 100 miles (161km). Beyond these are time-based formats (6hr, 12hr, 24hr), multi-day stage races, and extreme events exceeding 3,000 miles.
Ultra Marathon Distance Overview
| Distance | Kilometres | Miles | Avg finish time (recreational) | World record (approx.) |
|---|---|---|---|---|
| 50km | 50km | 31.1 miles | 5–8 hours | ~2:40–2:43 (men); ~3:04 (women) |
| 50 miles | 80.5km | 50 miles | 8–14 hours | ~5:50 (men); 5:18:57 Flower 2025 (women) |
| 100km | 100km | 62.1 miles | 10–16 hours | ~6:09 (men); ~6:33 (women) |
| 100 miles | 161km | 100 miles | 24–36 hours | ~11:51 (men); 12:37:04 Jennings 2025 (women) |
| 24-hour race | Variable | Variable | Top recreational: 120–180km | 340km+ (elite men) |
| 6-day race | Variable | Variable | Completion is the goal | 1,000km+ (elite) |
The 50km Ultra — The Entry Point
The 50km (31 miles) is the shortest distance generally accepted as an ultramarathon and the most logical first ultra for runners who have completed a marathon. At 8km beyond the marathon, it sounds like a modest step — and on a flat road course with good conditions, a runner with a 4-hour marathon base can approach it almost like a long training run with aid stations. In practice, most 50km races are trail events with meaningful elevation gain, which changes the experience significantly. A 50km trail race with 2,000 metres of climbing is a categorically different physical and logistical challenge from a flat road 50km.
The key shift at 50km is that running through it at continuous effort — the approach most marathon runners use — often doesn’t work. Walk-run strategies, regular food intake beyond gels, and deliberate pacing from the very first kilometre are the tools of ultra running that first become necessary at this distance. Most recreational runners complete their first 50km in 5–8 hours. On the performance end, Charlie Lawrence ran 2:49:02 as the men’s year-leader in 2025, and Gerda Steyn of South Africa ran 3:06:57 in the women’s field. World Athletics and the IAU both recognise 50km world records. For most runners, though, the first 50km is about finishing and learning what the distance demands. Our guide to marathon distances covers the physiology of running beyond 42km, which is directly relevant to first-time ultra runners understanding what changes beyond the marathon mark.
The 50-Mile Ultra — The First Real Test
At 80.5 kilometres, the 50-mile ultra is where the distance ceases to feel like an extended marathon and starts to feel like a fundamentally different kind of endeavour. Very few runners can run a 50-mile race without walking, eating solid food, and managing fatigue that accumulates over 8–14+ hours of continuous movement. The glycogen depletion issue that arrives in the final miles of a marathon is present much earlier in a 50-miler, and the body’s ability to process nutrition while continuing to move at sustained effort becomes a genuine skill to be trained rather than something improvised on race day.
The 50-mile distance requires a significant jump in training commitment compared to marathon preparation. Long runs must extend well beyond anything typical in marathon training, back-to-back long run days become necessary to simulate the fatigue of late-race running, and time on feet rather than pace becomes the primary training metric. The JFK 50 Mile in Washington DC (founded in 1963) is the oldest existing ultramarathon in North America. In 2025, Anne Flower set the women’s 50-mile world record of 5:18:57 at the Tunnel Hill 50 Mile in Illinois — running at 6:23 per mile for 50 miles, a performance that broke the previous record by nearly 13 minutes.
The 100km Ultra — The Unsung Distance
At 62 miles (100km), the 100km is simultaneously one of the most prestigious and least common ultramarathon distances. World Athletics recognises 100km world records, and the IAU 100km World Championship is the sport’s elite showpiece at this distance. Yet for all its prestige, the 100km is the least frequently organised of the four main ultra distances — most race directors focus on the more popular 50km, 50-mile, and 100-mile formats. In some ways, the end of a 100km race corresponds to where the hardest part of a 100-mile race begins — the final 60km of a 100-mile effort happens after the body has already covered 100km, which gives experienced 100km runners a visceral understanding of what 100-mile competitors are dealing with in the back half of their race.
Recreational runners typically complete the 100km distance in 10–16 hours. Elite performances approach 6 hours on certified flat courses — a pace of under 3:40 per kilometre sustained for 62 miles. The Tarawera Ultramarathon in New Zealand (through forests and along lake shores in the Rotorua region) is one of the most celebrated 100km events in the Asia-Pacific region.
The 100-Mile Ultra — The Iconic Distance
The 100-mile (161km) ultra is the distance most associated with the culture and identity of ultra running. It is the standard by which serious ultra runners measure themselves, the format that produces the sport’s most compelling race narratives, and the distance with the highest DNF (did not finish) rate of any standard ultra format. Most 100-mile races set cutoff times of 30–36 hours. Running at a pace that completes 100 miles in 30 hours means averaging roughly 18 minutes per kilometre — slower than a brisk walk — which conveys how much the body’s capacity for movement degrades over that duration and distance.
What makes 100-mile racing uniquely demanding is the sleep deprivation component. Almost no recreational runner completes 100 miles without running through at least one night, and for many it involves two nights of continuous movement. Managing the cognitive degradation that accompanies sleep deprivation — maintaining nutrition, navigating course markings, making decisions about pace and rest — becomes as important as the physical preparation. Hallucinations in the final third of a 100-mile race are not uncommon among sleep-deprived runners.
The Western States Endurance Run (through the Sierra Nevada mountains in California) is the world’s oldest 100-mile trail race, established in 1977. UTMB (Ultra-Trail du Mont-Blanc) — which covers approximately 171km through France, Italy, and Switzerland — is considered the world’s most competitive trail ultra, drawing elite fields from over 100 countries. Hardrock 100 in Colorado’s San Juan Mountains and Leadville 100 in the Colorado Rockies are among North America’s most storied 100-mile events.
In November 2025, Caitriona Jennings of Ireland set the women’s 100-mile world record of 12:37:04 at the Tunnel Hill 100 Mile — maintaining 7:34 per mile for 160 kilometres with metronomic consistency. Her performance followed Anne Flower’s course record at Leadville (17:58:19) earlier in the same year, a remarkable breakthrough season in women’s ultra running.
Time-Based Ultramarathons
A significant subset of ultra events are defined by time rather than distance. In a 24-hour race, competitors run as far as possible in 24 hours, usually on a loop course. In a 6-day race, the competition runs for six consecutive days with brief rest periods. The person who covers the most distance in the allocated time wins; everyone who participates completes an ultramarathon regardless of their final total.
Time-based events attract a different kind of ultra runner — those interested in maximising distance within a constraint rather than targeting a fixed finishing line. The IAU recognises world records for 6-hour, 12-hour, 24-hour, and 48-hour events. At the elite level, 24-hour event winners typically cover 260–280km for women and 280–310km for men. For recreational participants, a 24-hour event might mean completing 100–150km at a sustainable pace with planned rest breaks — still a meaningful ultramarathon achievement.
The Backyard Ultra
The backyard ultra is a relatively new format that has rapidly grown in popularity worldwide. Competitors run a loop of exactly 6.7km (4.167 miles) every hour, on the hour, for as long as possible. The winner is the last person still running when everyone else has dropped out. Because only one person can win — and that person must complete the final loop alone — backyard ultras theoretically have no fixed distance limit. The competition ends only when all but one competitor has stopped.
The format was invented by Gary “Lazarus Lake” Cantrell (the same person who created the Barkley Marathons) and has produced extraordinary distances. In 2025, Phil Gore of Australia ran 119 laps — covering nearly 798km — to set a new men’s backyard ultra world record at the Dead Cow Gully event. On the women’s side, Sarah Perry of the UK ran 95 laps (637km) at the Big Dog’s Backyard Ultra in 2025. Big Dog’s Backyard Ultra in Bell Buckle, Tennessee, is the sport’s flagship event.
Multi-Day and Extreme Ultras
Beyond the standard distances are events that push the definition of ultramarathon into multi-day territory. The Marathon des Sables covers 250 kilometres over six stages through the Moroccan Sahara, with competitors carrying their own supplies (food, sleeping gear) and the heat of the desert adding a survival element that distinguishes it from conventional ultras. The Spartathlon recreates the legendary 246km run of the messenger Pheidippides from Athens to Sparta, with a 36-hour cutoff that forces competitors to average faster than many recreational runners’ marathon pace — for five and a half marathon distances in a row.
Badwater 135 — 135 miles from the lowest point in North America (Badwater Basin, Death Valley) to the trailhead of Mount Whitney — is contested in July’s peak heat, with temperatures that can exceed 50°C on the course surface. The Self-Transcendence 3100 Mile Race in Queens, New York, is the longest certified footrace in the world: competitors run 5,649 metres (100 laps of a single block) per day for up to 52 days, covering 3,100 miles in total. It exists at the outer limit of what human beings have proven capable of achieving on foot.
The Barkley Marathons in Tennessee — approximately 100 miles over five unmarked loops with 60,000 feet of cumulative climbing through dense woods, with a 60-hour cutoff — occupies a category of its own. Entry is by secretive invitation. As of 2025, only 26 runners have ever completed the full course since the race began in 1986.
How to Choose Your First Ultra
For runners coming from a marathon background, the 50km is the natural starting point and the most forgiving introduction to ultra running’s demands. A runner who has completed a marathon in under 4:30 and maintains consistent weekly mileage of 50–70km has the physical base to complete a flat or moderate 50km with appropriate preparation. The key adaptations needed are nutritional (learning to eat real food while running and to fuel every 20–30 minutes rather than every 45–60), psychological (accepting that walking is part of the strategy rather than a failure), and structural (building the lower-leg and hip strength to handle hours of trail running rather than road running).
The 50-mile distance should be approached only after at least one successful 50km completion and a training block that extends long runs to 50–60km and incorporates back-to-back long run weekends. Attempting 100 miles without prior 50-mile experience is possible but significantly increases the risk of injury, withdrawal, and a negative first experience with the distance. Our guide to building mileage safely covers the structural progression that applies equally to ultra training, and our beginner running guide addresses the base-building that should precede any ultra distance training. Our race time predictor can give a starting point for estimating realistic ultra finish times based on your current marathon performance.
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FAQ: How Far Is an Ultra Marathon?
How far is an ultra marathon?
Any distance beyond 42.195km (26.2 miles). The shortest common ultramarathon is 50km (31 miles). The main standard distances are 50km, 50 miles (80.5km), 100km (62 miles), and 100 miles (161km). There are also time-based formats (6hr, 12hr, 24hr) and multi-day stage races. More than 600,000 people complete ultramarathons worldwide each year.
What is the most common ultramarathon distance?
The 50km is the most popular entry point. Among experienced ultra runners, the 50-mile and 100-mile are the most popular formats. The 100km is arguably the least common despite being a World Athletics-recognised world record distance with its own IAU World Championship.
How long does a 50km ultra marathon take?
Most recreational runners finish in 5–8 hours. Well-trained runners finish in 4–5 hours on flat courses. Trail 50kms with significant climbing can take 7–10 hours. Elite men run under 3 hours; elite women under 3:10. For first-timers, finishing comfortably and learning the distance matters more than targeting a time.
How long does a 100 mile ultra marathon take?
Most recreational runners take 24–36 hours. Experienced competitive runners finish in 14–22 hours. The women’s 100-mile world record is 12:37:04, set by Caitriona Jennings at Tunnel Hill, Illinois, in November 2025. Many 100-mile races have cutoff times of 30–36 hours, and DNF rates are substantially higher than at shorter ultra distances.
What is the longest ultramarathon in the world?
The Self-Transcendence 3100 Mile Race in Queens, New York — 3,100 miles over up to 52 days — is the longest certified footrace in the world. Among multi-day stage races, the Marathon des Sables covers 250km over 6 stages in the Moroccan Sahara. Among single continuous-effort races, Badwater 135 (135 miles) and Spartathlon (246km) are among the most demanding.
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