How many letters does the top answer for “on or of upper floors of a building” have?

The most common answer is upstair (7 letters).

Crossword clue: on or of upper floors of a building

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

upstair 7 letters wn-def

on or of upper floors of a building

upstairs 8 letters wn-def

on a floor above

on or of lower floors of a building 50% similar → downstairs