How Far Is an Ultra Marathon? Every Format¶
Anything longer than a marathon. The common distances are 50K, 50 miles, 100K and 100 miles, with 200 milers beyond that. Some races are set by time instead of distance: 12 hours, 24 hours, or a backyard loop every hour until one runner is left.
Below is what each of those looks like, for the marathoner whose friend just said "backyard ultra" and left it there.
What is an ultra race?¶
A marathon is 26.2 miles, or 42.195 kilometers. An ultramarathon is any footrace longer than that. The International Association of Ultrarunners uses the same literal definition, so a course a few yards past the marathon technically counts. In practice, races pick round numbers.
Here are the ones you will see most often, in miles so they are easy to compare against the 26.2 you know:
| Name | Kilometers | Miles |
|---|---|---|
| 50K | 50 | about 31 |
| 50 miler | about 80 | 50 |
| 100K | 100 | about 62 |
| 100 miler | about 161 | 100 |
| 200 miler | about 322 | 200 |
The 50K is the one most people start with. It is five miles longer than a marathon, which surprises people who expected a bigger jump. The distances after it get long quickly.
Ultras are also run on more kinds of ground than marathons. Many are on trails, with climbing, so the same distance can take far longer than it would on pavement. Many are run at a pace that includes walking the steep parts. A 100 miler can take a runner more than a day, and a 200 miler is more than one night out. That is why ultrarunners talk about hours on their feet more than they talk about pace.
None of this means an ultra is for someone else. A first 50K, a fifth hundred, and a return after a year off are all ultras, and they all start the same way: a person who ran a long way and wondered what came next.
What is a 100 mile race called?¶
A 100 miler. Runners also say "a hundred," or "a hundo."
There is no special title for the race beyond that. A race with "100" in its name is usually the distance in miles. A race with "100K" in its name is 62 miles. When a name has a number and no unit, check the race page, because the two are very different days.
Most people finish a 100 miler by walking and running through a full day and a night, and many take more than 24 hours. That is normal for the distance, and a finish is a finish whatever the clock says.
A 100 miler is a long way, but it is not the top of the list. Two hundred miles is a real race distance too.
What is a backyard ultra?¶
A backyard ultra has no fixed distance. Every hour, on the hour, every runner starts a loop of 4.167 miles (6.706 kilometers). Finish the loop inside the hour and you rest for whatever time you have left, then start the next one. Miss the hour and you are out. The event continues until one runner completes a lap alone, and that runner is the sole official finisher. Everyone else is recorded as a DNF, a did not finish.
The odd number is not arbitrary. It is 100 divided by 24, so 24 hours of loops adds up to 100 miles. The format started with Big's Backyard Ultra, created by Gary "Lazarus Lake" Cantrell in Bell Buckle, Tennessee, and many local races copy it.
What makes it different from every other ultra is that the field decides how long it lasts. Nobody picked a finish line. The race ends when the second-to-last runner stops, so the winner is the one person who ran a loop nobody else did.
For a runner, this is a different set of problems than a point-to-point 100. You never leave the start area, so your gear and food are right there. But you also cannot get ahead, because running faster just buys a longer rest before the next hour. The skill is staying steady for a long time, hour after hour.
Black Hills Backyard Ultra is one example, and it is in NavRun's race catalog.
What is the shortest ultramarathon?¶
By definition, anything past 26.2 miles. In practice, the 50K at about 31 miles is the shortest distance that is commonly raced. If a friend says they are running an ultra and does not say the distance, 50K is the most likely answer. If you have run a marathon, you have already done most of one. The extra five miles come at the end, when you are tired, which is the part that is new.
What about races set by time?¶
Some ultras are not about covering a distance at all. A timed race gives everyone the same clock, usually 6, 12 or 24 hours, and the result is how far you got. Runners usually go around a short loop again and again, so the course is simple and the same faces pass you all day.
The Mountaineer Rumble 12 Hour is a timed race in the catalog. On a loop course aid is never far, and nobody is stranded miles from the start. A timed race rewards what the sport rewards in general: staying out there.
The International Association of Ultrarunners keeps records for 6, 12 and 24 hour races alongside the distance ones, so timed racing is an established part of the sport and not a side format.
Why the distance is only half the question¶
Two 50Ks can be two different days. One is a flat loop on gravel. The other climbs for thousands of feet on rocky trail and closes its aid stations on a schedule. Race pages list both the distance and the climbing for that reason, and you will want both before you decide.
Most ultras also have cutoffs, which are times by which you must reach certain points. They exist for safety and for the volunteers, and a runner who knows the cutoffs ahead of time can plan around them. Timed races and backyard ultras work differently: the clock is the course, so there is no cutoff to chase, only an hour that keeps coming around.
Medical questions, such as whether your body is ready for a long day, belong with your doctor.
Where to find a race¶
NavRun's race catalog holds 891 races, and it has every format described above: distance races from 50K to 200 miles, timed races like the Mountaineer Rumble 12 Hour, and backyard ultras like Black Hills Backyard Ultra. You can browse it without an account at navrun.app/ultras.
If you are the marathoner with the friend, the useful move is probably to ask which format it is. "Backyard" means loops every hour. "12 Hour" means a clock. "100" means miles, and the number after it tells you how long they will be out. Then ask when you can show up. A runner on a loop course will see you every time around.
Find one near you. navrun.app/ultras