How many letters are there in English Vocabulary?

There's no single answer to how many letters are in the English vocabulary. Here's why:

* Vocabulary is constantly evolving: New words are added and some become obsolete.

* Letter vs. character: The English alphabet has 26 letters, but we also have special characters (like apostrophes, hyphens, etc.) that are used in words.

* Counting letters in a word vs. the whole vocabulary: Do we count the total number of letters used in all words, or only unique letters?

Here's what we can say:

* The English alphabet has 26 letters.

* There are many thousands of words in the English language, with a constantly growing number.

To give you a more specific answer, you'd need to define what you mean by "letters" and "vocabulary" and potentially specify a dictionary or word list.