How loud can A 30 watt amp get?

Could you please elaborate on the potential loudness capabilities of a 30-watt amplifier? I'm curious to understand if this amplifier's power rating translates to a specific decibel level or if it varies depending on the speaker's efficiency and other factors? Additionally, is there a general rule of thumb or a range of decibel levels that one might expect from a 30-watt amp under typical usage conditions?