ControllerColliderHit.moveLength

Description

How far the character has travelled until it hit the collider.

Note that this can is different from what you pass to CharacterController.Move, because all movement is constrained by collisions.

    function OnControllerColliderHit(hit : ControllerColliderHit) {
        Debug.Log(hit.moveLength);
    }

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void OnControllerColliderHit(ControllerColliderHit hit) {
        Debug.Log(hit.moveLength);
    }
}