Screen.width

説明

ピクセル単位のスクリーンの幅（読み取り専用）

This is the actual width of the player window (in full-screen it is also the current resolution).

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Example : MonoBehaviour
{
    void Start()
    {
        //Output the current screen window width in the console
        Debug.Log("Screen Width : " + Screen.width);
    }
}