Vector3.Distance

Description

Возвращает расстояние между a и b.

Vector3.Distance(a,b) is the same as (a-b).magnitude.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Transform other;
    void Example() {
        if (other) {
            float dist = Vector3.Distance(other.position, transform.position);
            print("Distance to other: " + dist);
        }
    }
}