The main difference between a marathon and a half-marathon is the distance: a full marathon measures 42.195 kilometers (26.2 miles), while a half-marathon is precisely half that distance, at 21.097 kilometers (13.1 miles). This distinction means that the training, pace, and strategies differ significantly between the two. Half-marathons are often seen as more accessible for beginners, while full marathons challenge even seasoned runners due to their endurance requirements.