In linguistics, vowel length is the perceived duration of a vowel sound. Often the chroneme, or the "longness", acts like a consonant, and may etymologically be one, such as in Australian English. While not distinctive in most dialects of English, vowel length is an important phonemic factor in many other languages, for instance in Finnish, Fijian, Japanese, Old English, and Vietnamese. It plays a phonetic role in the majority of dialects of English English, and is said to be phonemic in a few other dialects, such as Australian English and New Zealand English. It also plays a lesser phonetic role in Cantonese, which is exceptional among the spoken variants of Chinese.

Many languages do not distinguish vowel length, and those that do usually distinguish between short vowels and long vowels. There are very few languages that distinguish three vowel lengths, for instance Luiseño. Some languages, such as Finnish, Estonian and Japanese, also have words where long vowels are immediately followed by more vowels, e.g. Japanese hōō "phoenix" or Estonian jäääär "ice edge".