Loui, movies are produced at a certain loudness in the mixing studio and then put on a disc/streaming feed at that level. In turn, if a home theater is properly calibrated, the movie will replay at the very same level as it was produced. The actual level you are hearing at your seating depends on several factors, among others : Distance from the speakers, sensitivity of the speaker, amplifier gain, gain settings in the pre-pro and obviously the position of the volume knob! Since that one is constantly used and varied, you must establish a position for the knob at which your system will be at the same loudness as the studio and remember that setting for futur recall. If this is of any importance to you, that is!

We have adjustable gain parameters in the pre-pro and sometime on the amps themselve, so one may "decide" where he wants the volume position to be at the calibrated level.

I decided I wanted the main volume position to be at -10dB, so I used the gain trimmers on my amps to adjust the channels gain so the reference tone is at the correct level as measured in room at listening position. A Dolby compliant room should be able to reproduce the highest peaks at 105 dB SPL as measured at the listening position. The internally generated test tone is 30dB lower than that, so you adjust the actual sound in room to 75 dB SPL. As a side note, reference level is usually pretty loud, some people prefer to watch movie at a somewhat lower level than that.

This is pretty basic home theater audio stuff. You may find more detailed information, explained better too, on this topic, on the web!