What is an ultramarathon?

Maybe you've finished a marathon and caught yourself wondering what comes after it. Maybe a friend posted a photo from a 50K, muddy to the knees and grinning. Either way, the first question is simple: what is an ultramarathon, and how far does it go? An ultramarathon is any race longer than 26.2 miles. From there the distances run from 31 miles to races that last six days.

A lot of runners assume ultras are for a different kind of person. The data below paint a more ordinary picture: the average ultrarunner is in their early 40s, and the median finisher of one famous 100-mile race moves at about the speed of a brisk walk. What gets people to the start line is months of runs that fit around work and family.

Below are the standard distances, finish times, world records, who runs ultras, how training changes and what happens to your body. For the 26.2-mile basics, see our page on how long a marathon is.

What Counts as an Ultramarathon?

An ultramarathon, usually shortened to ultra, is any running race longer than the marathon's 42.195 kilometers (26.2 miles). There's no upper limit. World Athletics, the sport's global governing body, sorts ultra races into two types: those run over a set distance, such as 50 or 100 kilometers, and those run for a set time, such as 6 hours, 24 hours or several days. The International Association of Ultrarunners (IAU), founded in 1984 and affiliated with World Athletics, governs the sport and holds world championships at 50 km, 100 km and 24 hours every two years.

Ultras also differ by surface. Road and track ultras are measured like road races. Trail and mountain ultras follow dirt paths with big climbs, so the course shapes the finish time as much as the distance does. Multi-stage races split a long route into daily legs, and some cross whole countries.

Is a 50K considered an ultramarathon?

Yes. A 50K is 50 kilometers, which is 7.8 kilometers (4.85 miles) longer than a marathon, so it's the shortest of the standard ultra distances. It's also one of the three distances with an IAU world championship, alongside the 100K and the 24-hour race.

Ultra Marathon Distance: Every Standard Ultra in Miles and Kilometers

Ultras don't have one official length the way the marathon does, but a handful of distances come up again and again on race calendars. Here's how they compare:

Conversions are our arithmetic. Real courses often run a little off their name: the Western States course is 100.2 miles, and the Comrades Marathon in South Africa has measured anywhere from 86.8 to 90.2 kilometers in recent years.

The 50K is the usual first ultra because it's the shortest. A 100-mile race takes most finishers a full day or longer, so they run through the night with a headlamp.

Timed ultras and backyard ultras

In a timed race the clock is fixed and the distance is the result. Runners loop a track or a short course for 6, 12, 24 or 48 hours, or for six days, and the IAU lists a world record or world best for each of those durations. In a backyard ultra, runners start a loop of about 4.17 miles (6.7 km) at the top of every hour until only one runner is still going. Twenty-four laps make exactly 100 miles.

How Long Is a 50K?

A 50K is 31.07 miles, usually rounded to 31.1. The K stands for kilometers, so a 50K is 50,000 meters, about 54,681 yards or 164,042 feet. On a 400-meter track it would be exactly 125 laps. Next to a marathon, a 50K adds 7.8 kilometers, or 4.85 miles, a little less than an extra 8K race on top of 26.2 miles.

How long does it take to run a 50K?

The average finisher takes about 6 to 7 hours. The biggest dataset comes from Nikolaidis and Knechtle (2018), who analyzed 494,414 finishes of 50 km races worldwide from 1975 to 2016. Across all those years, men averaged 8.35 km/h and women 7.77 km/h. At those speeds a 50K takes about 5 hours 59 minutes for men and 6 hours 26 minutes for women.

The averages have slowed as the sport has grown. By 2016, men averaged 7.98 km/h and women 7.29 km/h, about 6 hours 16 minutes and 6 hours 52 minutes. The paper reports speeds, so these times are our arithmetic. Its data mix road and mountain races, and a hilly trail 50K can take hours longer than a flat one.

50K pace chart

If you have a finish time in mind, this chart turns it into the pace you'd need to average:

Average paces over 50 kilometers (31.07 miles), rounded to the nearest second. Time spent at aid stations counts toward your finish.

How Long Is an Ultramarathon?

In time, an ultramarathon lasts anywhere from under 3 hours for the world's fastest 50K runners to six days in the longest timed races. For everyone else, these landmarks from real races and studies show the range:

Sources: Nikolaidis and Knechtle (2018); the Comrades Marathon Association's 2026 race statistics; the Western States Endurance Run's statistics page; Millet and colleagues (2011); Saugy and colleagues (2013). The mountain races also have as much descent as climbing.

Distance alone doesn't set the time. The Tor des Géants is about twice as long as the Mont-Blanc race, but it took its finishers more than three times as long.

How long does a 100-mile race take?

Most finishers of a 100-mile trail race need about a day. Western States, run since 1974, starts at 5 a.m. and gives runners until 10:59:59 the next morning, just under 30 hours, to earn a finisher's award: a silver belt buckle under 24 hours and a bronze one under 30. Since 1986 its median finish has ranged from 24:48:29 to 28:15:00. The 2026 median of 25:41:34 works out to about 15:23 per mile, or 3.9 mph (our arithmetic), on a course that climbs more than 18,000 feet and descends nearly 23,000. The course records, both set in 2026, are 13:46:15 for men and 15:28:05 for women.

Ultramarathon World Records

The fastest ultra runners hold paces that most recreational runners couldn't keep up for a 10K. These are the world records and bests the IAU listed in May 2026:

Records as listed on the IAU records page, updated May 6, 2026, which also lists 6-hour and 12-hour marks and labels the six-day marks as world best performances rather than ratified records. Mile conversions are our arithmetic. Sorokin's 24-hour record works out to 7:15 per mile for a full day, and Bonne's six-day best to about 108 miles a day, close to 25 marathons in all.

How Many People Run Ultramarathons?

More every year, though it's still a small group. RunRepeat's State of Ultra Running report (Ronto and Nikolova, 2020) analyzed 5,010,730 results from 15,451 ultra races held from 1996 to 2018. Ultra participations per year rose from 34,401 to 611,098 over that span, an increase of 1,676 percent, and the number of individual runners grew from 24,102 to 329,584. Women made up 23 percent of participants by the end of the data, up from 14 percent at the start, and the average participant was 42.3 years old.

Ultra runners also hit their best later than marathoners. In the 50 km data, the fastest finishers were about 39 to 41 years old. A 2018 review by Knechtle and Nikolaidis in Frontiers in Physiology puts the best ultra performances at about 35 or older, against about 30 for the marathon, and the typical ultramarathoner at about 45. Some single races are huge: South Africa's Comrades Marathon started 20,349 runners in 2026.

What percentage of people can run 50K?

Nobody has measured it, so be skeptical of any percentage you see quoted. Finishing an ultra is still rare: about 330,000 different people completed one worldwide in 2018, by RunRepeat's count. That reflects interest and training time as much as ability. Someone who has finished a marathon can usually build to a 50K with a few more months of training, because the extra 4.85 miles are run slower and often with walking breaks.

How Is Ultra Training Different From Marathon Training?

Ultra training starts where marathon training leaves off. You need the same base of easy mileage, which our guide to how to train for a marathon builds. What changes is the goal: instead of holding a pace for 26.2 miles, you learn to keep moving for six hours or a full day over rough ground while eating.

Ultra runners train a lot, but not fast. In the ULTRA Study, a survey of 1,212 active ultramarathon runners, the median runner covered 3,347 km in the previous 12 months, about 40 miles a week (Hoffman and Krishnan, 2014; the weekly figure is our arithmetic). The Knechtle and Nikolaidis review notes that ultra runners log more weekly volume than marathoners but run it more slowly. In RunRepeat's data, runners' average pace improved by 12.3 percent between their first and 20th ultra.

1. Time on your feet replaces distance

Plan long runs by hours, not miles, because a rocky trail mile takes far longer than a road mile. For a first 50K, build the long run to about 4 to 5 hours of easy running and walking. Back-to-back long runs, such as 3 hours on Saturday and 2 on Sunday, teach you to keep going on tired legs without the recovery cost of one very long run.

2. Hike the climbs on purpose

Walking the steep sections is normal, even for strong runners. Once a week, hike hard up a long hill or stairs, leaning forward with your hands pushing on your thighs, then jog easily back down. In the strength studies below, the slower, more walking-heavy race was the easier one on the legs.

3. Prepare your legs for the downhills

Descents are harder on your legs than climbs. Your quadriceps work as brakes, lengthening under load with every step, which is eccentric muscle work. Build it with downhill running on gentle grades and with dumbbell or bodyweight split squats, step-downs and lunges two days a week.

4. Practice eating, night running and your race gear

Use every long run to practice the foods and drinks you'll race with. If your race runs past sunset, do some long runs with a headlamp. Many trail ultras require runners to carry set gear such as a jacket, water and a light, so check the rules early and train in it.

How long does it take to train for a 50K?

If you've run a marathon in the past year and still run 20 to 30 miles a week, plan on about 12 to 16 weeks of 50K-specific training. Coming from shorter races, build a marathon-level base first. A peak week for a first 50K might look like this:

This is a template, not a trial result. Build up to it over the first two months, and cut the volume by about a quarter every third or fourth week.

What Do Ultramarathon Runners Eat?

Ultra runners eat a lot of ordinary food, and they eat it while moving. The International Society of Sports Nutrition's 2019 position stand on ultramarathon nutrition (Tiller and colleagues) gives these targets for racing:

• Energy: about 150 to 400 calories an hour.
• Carbohydrate and protein: about 30 to 50 grams of carbohydrate and 5 to 10 grams of protein an hour, within those calories.
• Fluid: about 450 to 750 mL an hour, or roughly 150 to 250 mL every 20 minutes.
• Sodium: possibly more than most commercial sports products provide, meaning above 575 mg per liter.

Over many hours, real food is easier to keep eating than sweet gels alone, which is why trail aid stations often set out potatoes, fruit, salty snacks and broth. In training, the stand supports about 5 to 8 grams of carbohydrate per kilogram of body weight a day and about 1.6 grams of protein per kilogram. It also backs progressive gut training: practicing your race food on long runs so your stomach learns to handle it. Our guide to what to eat before a long run covers the meals before you start.

What Happens to Your Body During an Ultramarathon?

Ultras push the body further than any other common running event, so researchers study them closely. Here's what they've measured.

You burn far more than you can eat

The ISSN position stand estimates that a 50 kg (110 lb) runner burns about 3,460 calories in a 10-hour, 50-mile race, and a 70 kg (154 lb) runner about 9,890 in a 25-hour, 100-mile race. Covering that would mean eating close to 400 calories every hour for a full day. The Knechtle and Nikolaidis review notes that ultra runners generally can't eat enough during a race, so they finish with an energy deficit and lose some body fat and muscle.

Your gut often rebels

The ISSN stand calls 30 to 50 percent of runners a conservative estimate for gut problems during ultras. Among 272 runners at the Western States 100, 96 percent had gut symptoms at some point, and 44 percent said those symptoms hurt their performance. Long, hard running diverts blood away from the gut, which slows digestion, as our article on why you feel sick after working out explains.

Leg strength drops by a quarter to more than a third

Millet and colleagues (2011) tested 22 men before and after the 2009 Ultra-Trail du Mont-Blanc, a 166-km mountain race that took them 37 hours 37 minutes on average. Their maximal strength fell by about a third in the thigh muscles that straighten the knee and by nearly 40 percent in the calves, and part of that fatigue came from the nervous system rather than the muscle. Most strength came back within two days, but full recovery took 16.

Longer isn't always harder on the muscles, though. Saugy and colleagues (2013) tested runners after the Tor des Géants, about 330 km with about 24,000 meters of climbing. Their strength fell by 24 percent in the thighs and 26 percent in the calves, less than after the Mont-Blanc race, and the authors credited the slower pace and the lower mechanical stress of walking.

Muscle damage, kidneys, the heart and sodium

The Knechtle and Nikolaidis review reports creatine kinase, a blood marker of muscle damage, reaching 100,000 to 200,000 U/L after an ultra, depending on fitness and race length. Kidney function often dips temporarily, and the review puts acute kidney injury at nearly half of ultra runners in the studies it covers. Troponin, a marker of heart muscle strain, rises after a race. If you have heart or kidney problems, talk to your doctor before training for an ultra.

Drinking far more water than you lose can dilute the sodium in your blood, a condition called exercise-associated hyponatremia. The review reports it in about 30 percent of runners in some 100-mile races, but in no more than about 8 percent at ultras held in Switzerland. Stay roughly within the ISSN's hourly fluid range rather than forcing extra water, and take some sodium on long, hot days.

Recovery takes weeks, not days

Strength in the Mont-Blanc study took 16 days to return, so give yourself at least a couple of easy weeks after a 50K and more after a 100-miler. Our page on how long it takes to recover from a marathon covers the first weeks after a long race, and our review of compression boots includes a randomized trial in runners who had just finished a 161-km race.

Are Ultramarathons Bad for You?

For healthy, well-prepared runners, the evidence doesn't show that they are, but it doesn't show that more is better either. Among the ULTRA Study's 1,212 runners, chronic diseases were generally less common than in the general population, with asthma and allergies as the exceptions. They missed an average of 2.2 days of work or school a year to illness or injury, against 3.7 days for employed U.S. adults.

The costs show up as injuries. In the year before the survey, 77 percent had an exercise-related injury, most often at the knee, and 5.5 percent had a stress fracture. And 4.9 percent said they had been hospitalized after a race, mostly for dehydration, electrolyte problems or heat exhaustion. The survey only reached people still running ultras, so anyone who had quit because of health problems wasn't counted.

What is the healthiest distance to run?

There isn't one, and you don't need ultra distances for health. Lee and colleagues (2014) followed 55,137 adults for about 15 years. Runners had a 30 percent lower risk of death from any cause and a 45 percent lower risk of cardiovascular death than non-runners. Even 5 to 10 minutes a day at speeds under 6 mph was linked to the benefit, and it was similar at lower and higher weekly amounts. The biggest benefit went to people who kept running over about six years, so for health, sticking with it matters more than how far you go.

What This Means for You

The numbers to remember are short. Anything past 26.2 miles is an ultra, a 50K is 31.1 miles, and the average 50K finisher takes about 6 to 7 hours. If you've run a marathon, a flat or gently rolling 50K is the natural next step. Start by stretching your long run toward 4 hours, hiking the steepest hills on purpose and practicing your race food on every long run.

What decides a first ultra is the four months before it, and that's where most attempts quietly stall. A missed long run becomes a missed week, and the strength sessions are the first thing to go. That's a consistency problem, and willpower is a poor fix for it. A routine with some pull to it works better. As Katie put it: "I've tried everything. This is the first time I've stuck with something past two weeks."

If the strength and mobility days are the ones you'd skip, a workout app that keeps you motivated can carry them for you. In FitCraft, 3D AI coaches demonstrate each dumbbell and bodyweight exercise and lead mobility and yoga sessions, and your coach says your name during the workout. Streaks and programs keep those sessions on the calendar, and the workouts adjust as you progress.