Quick and dirty way to count frames per second (FPS) on Unity

FpsCounter.cs

using UnityEngine;

public class FpsCounter : MonoBehaviour
{
    float prev = -1;
    float fps = 0;

    void Update()
    {
        var now = Time.realtimeSinceStartup;
        if (prev >= 0)
        {
            float fpsNow = 1 / Mathf.Max(0.001f, (now - prev));
            fps += (fpsNow - fps) * 0.05f;
        }
        prev = now;

        if (Time.frameCount % 100 == 0)
        {
            Debug.Log("FPS: " + fps);
        }
    }
}