Mathf.NextPowerOfTwo

public static int NextPowerOfTwo (int value);

Description

Returns the next power of two that is equal to, or greater than, the argument.

using UnityEngine;

public class ExampleClass : MonoBehaviour
{
    void Start()
    {
        //Prints 8 to the console
        Debug.Log(Mathf.NextPowerOfTwo(7));

        //Prints 256 to the console
        Debug.Log(Mathf.NextPowerOfTwo(139));

        //Prints 256 to the console
        Debug.Log(Mathf.NextPowerOfTwo(256));
    }
}