It is difficult to say precisely how far fleeing troops will run because they are no longer fighting as a body but milling around in a frightened mob. To represent this, dice are rolled to establish how far the fleeing unit moves: if the unit normally moves 6" or less, roll 2D6; if the unit moves more than 6". roll 3D6. The result is the flee roll, which is the distance covered by the fleeing troops.
Determine the distance fled by each unit fleeing from the combat, but do not move the models yet. If there were many units involved in the same combat, it helps to leave the dice showing the flee distance next to each unit.