How many letters does the top answer for “being in the exact middle” have?

The most common answer is middlemost (10 letters).

Crossword clue: being in the exact middle

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

middlemost 10 letters wn-def

being in the exact middle

midmost 7 letters wn-def

being in the exact middle

the quality of being exact 50% similar → exactitude, exactness