二 or 两

Chinese has two words for 'two'. Use 两 (liǎng) to say how many: before a measure word or a time word, e.g. 两个人 (two people), 两本书 (two books), 两天 (two days), 两年 (two years), 两岁 (two years old). Clock times work the same way: 两点 (two o'clock).

Use 二 (èr) when two is a digit or a position:

• counting and maths: 一、二、三; 一加一等于二
• inside larger numbers, even before a measure word: 十二个 (12), 二十 (20), 九十二 (92)
• order and rank: 第二 (second), 二楼 (floor 2), 二年级 (year 2)
• dates and weekdays: 二月 (February), 五月二号 (2 May), 星期二 (Tuesday)
• digits read one by one: 二零二六年 (2026)

Before 千 and 万 people usually say 两 (两千, 两万); before 百 both 两百 and 二百 are fine.