using UnityEngine;
private float ratio = 1f;
private float panelW;
private float panelH;

UIRoot root = GameObject.FindObjectOfType<UIRoot>();
if (root != null) {
    // 实际尺寸和设计尺寸比例
    ratio = (float)root.activeHeight / Screen.height;            
}

// 设计尺寸
panelW = transform.GetComponent<UIPanel>().width;
panelH = transform.GetComponent<UIPanel>().height;

// 实际尺寸
width = panelW * ratio;
height = panelH * ratio;