What determines the volume of a Turntable?

Also, the recording itself is variable in that some are recorded more softly/loudly than others, and the speed of the record too has an effect. 45's are louder than 33's

yeah everything in your chain on such a tiny signal will alter it somewhat all the way to speaker sensitivity. Also cables and how good they are can effect the energy you get out of this tiny vibrating signal coming all the way from that little needle in the groove... Warning some Albums are just lower output too, so don't expect consistent gain/volumes out of all vinyl just the same as CD has no real standard in output.

First off, you never want to be able to hear your turntable!

But I think what you are asking primarily relates to the combination of phono stage gain (dB) and cartridge output (mV). A search will find calculators for best matches such as the KAB site Dougdeacon suggests. As a general rule and starting point, moving magnet and high output moving coil cartridges with >1.0 mV output may work into a standard built-in phono stage. A medium or low output moving coil cartridge (not as likely a match in your system) with <1.0 will require an additional gain section (active or transformer) either built-in or inserted ahead of your standard phono stage.

The three dimensional space it displaces.