How many letters does the top answer for “the outside boundary or surface of something” have?

The most common answer is fringe (6 letters).

Crossword clue: the outside boundary or surface of something

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

fringe 6 letters wn-def

the outside boundary or surface of something

periphery 9 letters wn-def

the outside boundary or surface of something

the boundary of a surface 50% similar → edge