Mathf.PI

public static float PI ;

説明

円周率（ 3.14159265358979... ）（読み取り専用）

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public float radius = 5;
    void Start() {
        float perimeter = 2 * Mathf.PI * radius;
        Debug.Log("The perimeter of the circle is: " + perimeter);
    }
}