两 vs 二 in large numbers

Question

What are the exact rules for choosing between 二 and 两 for writing large numbers (larger than 11)? What I understood was:

0. For things like serial numbers, codes, where the number is written or read using its digits without the words like 十，百，... always use 二 (and may use 幺 instead of 一)。
1. At the last (units) place, always use 二. E.g. 342 是 三百四十二。
2. Before 十 always use 二. E.g. 325 是 三二五。
3. Before 百，千，万，亿 always use 两。 E.g. 2231 是 两千两百三十一。 So, 2222222 是 两百二十两万两千两百二十二, right?

The reason I started to doubt it is that both Deepl and Google Translate disagree with the last one translating 2231 as 两千二百三十一 (while 231 is still 两百三十一). One option to accommodate that is to change rule 3 to

3'. Before 百，千，万，亿 use 两 when it is the first digit of the number, otherwise use 二. E.g. 2231 是 两千二百三十一。

I'm not sure if that is the correct thing to do, though.

What are the correct rules then?

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There are 2 similar questions, but the answer there address more broad rules for 二 vs 两 and do not appear to cover the rules for large numbers.

1. Difference between 两 and 二?
2. Number two in chinese: 二 vs 两

Answer 1

0. For things like serial numbers, codes, where the number is written or read using its digits without the words like 十，百，... always use 二 (Not necessarily true - 2202 can be read as 二二零二 or 两两零二. See rule 1 for the last digit that contains 2.)

1. At the last (units) place, always use 二. E.g. 342 是 三百四十二。(Correct, bur redundant, see modified rule 2.)

2. Before and after 十 always use 二. E.g. 322 是 三百二十二。

3. Before 百，千，万，亿 always use 两。(Wrong) E.g. 2231 是 两千两百三十一, also fine are: 二千两百三十一, 二千二百三十一, 两千二百三十一.

So, 2222222 是 两百二十两万两千两百二十二, right? (No, per rule 2, it should be 两百二十二万两千两百二十二, or as noted in rule 3 - 二百二十二万二千二百二十二, and 两百二十二万两千二百二十二.)

Answer 2

There's no rules for choosing between 二 and 两, but more of the regional customary expression, although 两 is used more frequently orally to my intuition.

However, indeed the 二 is usually used at the last (smallest two, especially when two is the ending number), and 两 is usually used at the beginning (biggest two, especially when two is the leading number).

Still, instinct language feeling, no rule.

Answer 3

Confirm with your rules 0 and 1, but there are more to say to the other two rules.

Officially use 二 in all positions. Exceptions includes those 百，千，万，亿 without 零数 or before a head noun(二百人）, that is 200 两百, 2000 两千 etc. Examples of 零数 includes 220 二百二十，202 二百零二，more than 200 people 二百余人.

In accounting always use er (though a capital character is used but still readers er).

Colloquially 两 is widely used. Its usage varies regionally, but in general, starting from 百, the highest digit 2 is usually 两, and the lowest two digits are always 二, that is 二十二, while in the middle they are interchangeable.

The last two digit rule is used in groups, it applies also to cases before other units, like 二十二万、二十二亿, only 二 can be used. The highest digit rule is overwritten.

22,2222,2222 二十二亿两千两百二十二万两千两百二十二 all 两 can be replaced by 二

Answer 4

I think it is safe to say that you will almost always use 兩 with measure words, or in phrases like 一兩（one or two ) 兩三 (two or three) etc.

You will almost always use 二 in regular counting/serial number reading, ordinal numbers, and maths.

There are set phrases with either depending on the saying.

Everything else is a little more forgiving, or at least possibly varying from area. For example I have experience with a southern area where 二 is almost never used outside of what was just listed. However this is also the type of area to avoid erhua sounds and I wouldn't be suprised if areas more friendly to the sound used 二 more. Looking up random examples in long form numbers, I see some use of 二 when I would normally use 兩。

Also sometimes I will see 二 where I would consider it an ordinal number, but there is no 第. It should be clear in context but thought I'd mention it as a possible point of confusion.

If you have a specific area in mind, I recommend seeing how the words are used there. If not, then you can learn from a reputable source and as long as you are consistent in your usage no one will think it wrong, at most they will recognize it as a different area or maybe even the specific area. Comprehension should not be an issue.

Make sure to be self consistent with one way of speech and you will be good to go in general, its only when people mix different areas or are inconsistent that there are issues. For example erhua with taiwanese pronounciation (extreme example, most variations are a lot more subtle).