How to calculate FPS in this situlation?

I read some article about calculating fps but they seems just to get time and divide by frames.
It’s very weird because my monitor did not show any new scene until the last one. What I want is the real fps which means the next texture is exactly shown and this can be count one frame. How can I do this?
Thank you very much!!!

If you divide the time it took to render x frames with x you get the average FPS and there is nothing wrong with that value, you can do it like that or simply measure the time between the frames to get actual rendering time for each frame.