The most common letter in the English language is E.
Frequency studies count how often letters occur in written English, and E consistently ranks first in ordinary text corpora. Its high frequency is partly explained by common grammatical endings such as “-ed” and “-er,” frequent words such as “the” and “be,” and the large number of English words containing the letter. One widely cited estimate places E at about 12.7% of letters in general English text.
The result depends somewhat on what is counted. A dictionary, a newspaper, a novel, a technical corpus, and a list of word lemmas can produce different percentages and occasionally alter the ordering of less frequent letters. The standard answer remains stable because E is exceptionally common across many representative samples.
E is also important outside ordinary spelling. Al-Kindi used letter-frequency analysis in the 9th century to help break substitution ciphers, and modern cryptanalysts still use frequency patterns. The letter’s dominance also explains why lipograms—texts deliberately avoiding a letter—often target it.