Basic Rules to Use "二" and "两"

In Chinese, there are two words for“two”: 二（èr) and 两(liǎng), and Chinese learners are often confused about when each of them should be used. Today, we will illustrate the differences between them.

The major difference between them is that "二" is generally used when counting numbers (一、二、三,…), or performing mathematical computations. 两(liǎng) is used in front of measure words to express a quantity. For example:

两个苹果(liǎng gè píng guǒ) two apples
两张桌子(liǎng zhāng zhuō zǐ) two desks
两本书(liǎng běn shū) two books
两点钟(liǎng diǎn zhōng) 2 o’clock

"二" (èr) is also used as an ordinal number or in maths to indicate a numeral, a fraction, or a decimal. For example:
第二(dì èr) the second
二楼(èr lóu) the second floor
二分之一(èr fēn zhī yī) 1/2
零点二 (líng diǎn èr) 0.2

In the multi-digit numbers,
For tens place and ones place, we onLY use "二". Eg. 22(二十二)
Before the hundred(百), we can use either "两" or "二". e.g. 200(二百/两百).
When used before the thousand(千), ten thousand(万） or hundred million(亿), "两" is much more frequently used.
e.g. 2000(两千); 22222(两万两千二百二十二); 200,000,000(两亿)

When you want to say an approximate number, you can use "两". For examples
一两天(yī liǎng tiān) One or two days.
两三回 (liǎng sān huí) two or three times