Table adopted from Nau (1998:6)
Latvian has six vowels, with length as distinctive feature:
/? ?:/, and the diphthongs involving it other than /u?/, are confined to loanwords.
The vowel length ratio is about 1:2.5. Vowel length is phonemic and plays an important role in the language. For example, koka ['ku?ka] means 'made of wood', kok? ['ku?ka:] means 'on the tree'; pile ['pile] means 'a drop', and p?le ['pi:le] means 'a duck'.
Latvian also has 10 diphthongs (/ai ui ?i au i? u? iu (?i) ?u (?u)/), although some diphthongs are mostly limited to proper names and interjections.
Standard Latvian and, with a few minor exceptions, all of the Latvian dialects, have fixed initial stress. Long vowels and diphthongs have a tone, regardless of their position in the word. This includes the so-called "mixed diphthongs", composed of a short vowel followed by a sonorant. There are three types of tones:
Besides the three-tone system of the standard variety, there are also Latvian dialects with only two tones: in western parts of Latvia, the falling tone has merged with the broken tone, while in eastern parts of Latvia the level tone has merged with the falling tone. Hence, the Central Latvian tra?ks, dràugs, raûgs correspond to Western Latvian tra?ks, draûgs, raûgs, and to Eastern Latvian tràuks, dràugs, raûgs.
Latvian roots may alternate between [v] and [u] depending on whether the following segment is a vowel or a consonant. For example, the root Daugav- ('Daugava River') in the nominative case is [dau?av?], but is pronounced [dau?aupils] in the city name Daugavpils. In this example, the vocalic alternant [u] is realized as the off-glide of the diphthong /au/. However, when following a vowel that does not form an attested Latvian diphthong (for example, [iu]), [u] is pronounced as a monophthong, as in [zius] ('fish-NOM.SG.'; cf. [zivis] 'fish-NOM.PL.').