# Chinese numerals or Arabic numerals?

In formal writting in Chinese, should we write

or

or

Which one is considered more standard?

• As a matter of practicality, I don't think we would write It's been twelve thousand, three hundred and forty five days since that matter has occurred in English either. Commented Apr 7, 2019 at 3:05
• Arabic numerals have been incorporated into many languages, when we see sentence like "My phone number is 001-2000-110" we would read it as "my phone number is zero zero one- two zero zero zero- one one zero" but we would never write it that way. The same is true in Chinese
– Tang Ho
Commented Apr 7, 2019 at 4:28
• When writing Chinese vertically, Arabic numerals are less suitable. I have vertically-written Chinese books where even the page numbers are in vertically-written Chinese numerals!
– Flux
Commented Apr 7, 2019 at 5:58
• You may sometimes see numerals like this: 1万2345
– fefe
Commented Apr 8, 2019 at 1:22
• The last form is not proper here, you may only use seperator in articles of maths or scicence industries. The first two forms are acceptable, but you'd better use digits for small numbers (using 20 instead of 二十) while Chinese characters for large numbers (using 1.2 万 or 一万二/一万二千/一万两千 instead of 12000). Commented Apr 8, 2019 at 13:39

In formal writing in Chinese, should we write 事情已经过去了一万二千三百四十五天。

Only when you are writing in vertical writing format -- from top to bottom, right to left in columns

As for horizontal writing format like English, when we see sentence like "My phone number is 001-2000-110" we would read it as "my phone number is zero zero one- two zero zero zero- one one zero" but we would never write it that way. The same is true in Chinese if you write horizontally

If you write horizontally, it should always be:

If you write vertically, it should always be:

In terms of formality, I would say the first one (事情已经过去了一万二千三百四十五天) is more formal. That's what I was taught from school.

As a Chinese, I would say that NO ONE CARES if you wrote "一万二千三百四十五" or "12,345".
The first one is written in Chinese numerals, the second one in Arabic numerals, they are much pretty the same.
If you insist on writing Chinese numerals, I would recommend you do say "事情已經過去了超過一萬天", if you want to emphasize that the event has passed for a long time.