The "K" stands for kilometer. A kilometer is 0.62 of a mile, which makes a 5K race 3.1 miles long or 16368 feet long or 5000 meters long. When you hear about races such as the Carlsbad 5000, Santa Monica 5000 or Reno 5000, you can know that it is a 5K or 3.1-mile distance event.