How many letters does this word have?

The longest word appearing in major English dictionaries has 45 letters and reads pneumonoultramicroscopicsilicovolcanoconiosis, referring to a lung disease caused by inhaling very fine silicate or quartz dust, particularly the kind produced by volcanic ash. Its construction from Greek and Latin word parts allowed it to be built into an unusually long single term.

Neither 20 nor 100 letters accurately describes this word, 20 letters would be far too short to capture the full technical term, while 100 letters would vastly overshoot even this famously long entry, which sits precisely at 45 letters as documented in reputable dictionaries.

Many linguists and medical professionals suspect this word was coined partly as a deliberate exercise in constructing the longest possible medical term, rather than emerging naturally from ordinary clinical usage, and in practice doctors typically just refer to the underlying condition using shorter, more practical medical terminology.