Many years ago it was often said that the span from one's elbow to the tip of outstretched fingers should equal the distance from nose of seat to the handlebars.

This is still a somewhat usable, though extremely rough guide for horizontal measurements.

An equally old and unsophisticated rule for the vertical measurement only applies to traditionally designed "diamond" frames, and called for one-inch clearance of crotch from top tube, for obvious reasons.

Obviously seat-height is a different question.