* The monarch goes by a title that usually translates as "emperor" in English, and/or is accepted as the equivalent of   "emperor" in international diplomatic relations;
* The monarch rules (de facto or nominally) over other monarchs, without stripping monarchy-related titles from    these subjects ("vassals" or non-sovereign monarchs);
* The monarch rules several formerly sovereign countries, or peoples from different nations or ethno-cultural    provenance.
* The monarch assumes divine or other high-ranked religious characteristics.
* European (Christian) tradition: The monarch traced his imperial title to Roman precedent or recognition by a Roman   (Byzantine) emperor or supreme ecclesiastical official, see also: translatio   imperii.

Where the title chosen by the monarch has become a separate concept in the English language, the distinction whether this monarch would have been an "emperor" or a "king" is often no longer made: for instance caliph, sultan or khan as a concept of a type of monarch is usually defined separately, making it redundant to apply the emperor/king distinction to these types of monarchy.