How much volume does mastering add?

[Ocelots Revolver]

So I'm trying to A/B with mastered tunes I like to get my mixdown right. I don't have proper monitors so getting the low end is tricky and I'm using the visual reference of a spectrum.

Any clue how much db mastering adds to tracks? I understand it may depend on the track, but if their kick is peaking at -12 and mine is clipping the limiter at -18...

[SunkLo]

How long is a piece of string?

You can't really go by a spectrum analyzer. Your kick is more than 90hz rumble. Evidently if it's clipping your limiter, it's at more than -18dB unless your limiter threshold is set to -19dB. If you're monitoring the kick in context with the rest of the track you have to consider all the material from the other instruments. Since you're focusing on getting the low end right you should be high passing everything that doesn't need lows. You should also be analyzing your arrangement. Is a bunch of shit playing at once and eating up headroom? You can get by with sidechaining and general compression but the clearer your mix without those, the better it'll ultimately sound.

Match subjective volume for A/B tests. If you want to try and compare dynamic ranges, get a dynamic range meter and compress your master until they're matched up. Then you can hear how clear your mix will sound at an equivalent amount of squashing. Also make sure you're not A/Bing with some dodo's track that's been overcompressed. Your main concern in mixing is clarity. Compressing should be done at this stage mainly to rein in errant dynamics, to bring certain tracks forward that are too weak, and as a creative effect. Don't really worry about volume.

[Ocelots Revolver]

I appreciate the comment and the bit about dynamic range, but I'm well acquainted with the basics of mixing.

The problem is I can't hear the sub frequencies accurately so the only solution I see is to adjust those frequencies by sight, A/Bing a track I like for accuracy.

The problem with that is my reference track has been mastered, so the levels are not realistic. I notice things in common with most pro tracks like the subs and kick tend to peak at around 12 dB.

How do I adjust those values for my track?

[SunkLo]

Lowpass your master and your reference track after volume matching them. Then you can use your dynamics meter to suss out how much compression is going on. If you're just trying to balance your low freqs with respect to the rest of the track, volume doesn't really come into play at all.

[test_recordings]

It might be better to get a relative balance between elements rather than getting them at exactly the same volume level. I normally balance the bass to the kick then group them so I don't have to tweak them both separately later. The decibel level isn't so important for mixing as it long as it's not clipping because other factors like the psychoacoustic effects of compression, frequency content etc affect how people perceive it.