How many 13-letter words are there?

7,827 in the Tournament dictionary, which is the public-domain ENABLE word list. The Broad dictionary adds more.

What is the highest-scoring 13-letter word?

RAZZAMATAZZES at 51 points, counting tile values with no board multipliers.

No. The page shows the 300 highest-scoring; the pages linked below break the full list down by starting and ending letters.

7,827 words are exactly 13 letters long. RAZZAMATAZZES scores highest at 51 points.

Showing the highest-scoring of 7,827 words. The pages linked below split the rest into smaller lists.

Counting them, 13 letters gives 7,827 valid words — a large slice of English, and the ones worth the most points are at the top.

The distribution peaks at 13 letters (7,827 words) and thins out toward 13, where only 7,827 remain.

The most valuable word in this set is RAZZAMATAZZES at 51 points. It tops both tables: 52 in Words With Friends as well.

The longest answers are RAZZAMATAZZES, EMBEZZLEMENTS and KATZENJAMMERS, at 13 letters.

The solver above accepts the same query with extra filters, which is the quickest way to narrow a list this size.

squeezability: the property of being able to occupy less space
psychoanalyze: subject to psychoanalytic treatment
isocarboxazid: a monoamine oxidase inhibitor (trade name Marplan) that is used to treat clinical depression
schizophrenic: suffering from some form of schizophrenia
brachycephaly: the quality of being brachycephalic

How many 13-letter words are there?: 7,827 in the Tournament dictionary, which is the public-domain ENABLE word list. The Broad dictionary adds more.
What is the highest-scoring 13-letter word?: RAZZAMATAZZES at 51 points, counting tile values with no board multipliers.
Are all of them listed here?: No. The page shows the 300 highest-scoring; the pages linked below break the full list down by starting and ending letters.