Why is う sometimes read as "o" instead of "u"?


As an example, きょう is read as "kyoo", despite the last kana being usually read
as "u".

Why and when does this happen?




In most cases う after お、こ、そ、と、の、ほ、も、よ、ろ makes "o" sound longer.

For example: こうえん（kōen)、きょう (kyō)

There are some cases in which お is used to make "o" longer.

For example: おおきい (ōkii)、とおい (tōi)

There are also cases in which う is a suffix and read as う。

For example: おもう（omou、[思う]{おもう})

Learn more about long vowels.

P.S.: ō is for long "o", same as "oo".

