Technically, an ultramarathon is any foot race that extends beyond the standard marathon distance of 26.2 miles. Ultramarathons can be any distance above the marathon, with no upper limit.
Though ultramarathons can take place at any distance that exceeds that of a traditional marathon, there are some common ultramarathon distances, the lowest of which is 50 kilometers, or 31.069 miles. Fifty mile, 100 kilometer (62.137 miles) and 100 mile ultramarathons are also popular. Sometimes, these races are marked by time rather than distance, such as a 24-hour race. These races can be held in locations with extreme weather conditions or on trails with elevation changes as an additional test of endurance.