How many letters does the top answer for “classified according to various criteria into successive levels or layers” have?

The most common answer is hierarchal (10 letters).

Crossword clue: classified according to various criteria into successive levels or layers

hierarchal, hierarchic, hierarchical.

3 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

hierarchal 10 letters wn-def

classified according to various criteria into successive levels or layers

hierarchic 10 letters wn-def

classified according to various criteria into successive levels or layers

hierarchical 12 letters wn-def

classified according to various criteria into successive levels or layers