I believe -18 and -20 dBFS are the 'standard levels'. However, one has to consider the actual 'mixing' room that one is attempting to mix in, and set the audio system with that 'room' in mind.
For example, one reads for a 'real' mixing stage, 85 dB-C SPL is the reading one should have at the 'listening' point, for a 1K Hz tone @ -20 dBFS... but if one has a small room, such as a 10x10 'office', one should have the audio system adjusted to have a 79 dB-C SPL.
For ordinary mortals the Radio Shack SPL meter is sufficient, it's about $50.
Since my goal is for 'fest/Internet', I only think in terms of 'traditional' stereo or mono, dialog centered, sound mixing (mono... if Woody Allen can still put out everything he makes in mono, why can't I... and of course Saint Kubrick also went with mono for many of his films...). In order to get 'dolby' or other big league audio formats, the equipment, mix room certifications, etc. is far and away 'overkill' and expensive.
On units... there are a number of dBxxx units. So I'm using dB Full Scale, which is more typical in digital NLE's, and what I use since I don't have external audio meters in the various other units of sound measurement, other than the Radio Shack SPL meter.
Edited by jeclark2006, 22 August 2014 - 01:42 PM.