半(bàn) - half, semi-, half past in Mandarin

半 (bàn) is half, and where it sits in the phrase decides what it means. Before a measure word it means half of one thing: 半个小时 (bàn gè xiǎo shí) half an hour, 半杯水 (bàn bēi shuǐ) half a glass of water. After a number and measure word it adds a half on: 一个半小时 (yī gè bàn xiǎo shí) is an hour and a half.

That word order is the trap, because English puts "and a half" at the end in both cases. 两年半 (liǎng nián bàn) is two and a half years, while 半年 (bàn nián) is six months. Read the position, not the translation.

With clock time 半 (bàn) means half past: 七点半 (qī diǎn bàn) is half past seven. It also prefixes words in the sense of semi- or partly, as in 半天 (bàn tiān), half a day, which in speech usually just means ages.