A half marathon is an exact 13.1 miles or 21 kilometers. It is half the length of the full marathon, which is 26.2 miles or 42 kilometers.
In 2008, Running USA reported that the half marathon is the fastest-growing type of race. The reason for the increase in popularity of the half marathon is that while it is still challenging for the runner, it does not require as much training as a full marathon. The half marathon is generally run on streets and is often held concurrently with a marathon by using either late starts or early finishes for those not running the full marathon.