What is the most common vowel sound in English?

The most common vowel sound in English is the schwa, represented in the International Phonetic Alphabet by /ə/.

Schwa is a mid-central, usually unstressed vowel heard in words such as the first syllable of “about,” the second syllable of “sofa,” and the final sound of “comma.” Because it is produced with the tongue near the center of the mouth and little muscular tension, it often sounds short and indistinct.

Schwa is a sound, not simply a spelling pattern. Any vowel letter can represent it in an appropriate word: the a in “about,” o in “harmony,” u in “medium,” e in “taken,” or i in “pencil.” Conversely, the same letter can represent many other vowel sounds. This is why English spelling does not reliably reveal pronunciation.

The name comes through German from the Hebrew term shva, associated with reduced or absent vowel marking. In rhotic English accents, an r-colored schwa may occur in words such as “water” or “standard.” Schwa is especially important in speech rhythm because unstressed syllables commonly reduce toward it.