# When should I use 兆 instead of 万亿?

In the following sentence:

In this sentence, 万亿 is used instead of 兆, to express 10^12 digit.

So when should I use 万亿 and when 兆 to express such a large number?

And also what about the case to express more than 万亿, such as 10^16?

Japanese use 万, 亿, 兆, 京... but how about Chinese? Should I write it as 91万万亿2513万亿522亿6915万159 to express 912513052269150159? or 91京2513兆522亿6915万159?

I am a Chinese PhD student studying computer science and communication engineering in London. I guess I might be the right person to give you the answer.

• This is incorrect. In computer science context, 兆 is only used for Megabytes, where 兆 is a million, not a trillion. This is consistent with physics terms like Megahertz is called 兆赫 etc. In computer science, 一万亿 = 1 trillion is called 1T in Chinese. – NS.X. Jul 6 '19 at 8:46
• 兆 is for the metric prefix "mega-" (for a million), such as 兆字节 (megabyte) and 兆赫 (megahertz). 万亿 is for a trillion. The metric prefix for a trillion is 太 (tera-), such as 太字节 (terabyte). – Victor Nov 28 '19 at 12:06
• Indeed, it is a trillion, not a million. – Tianhao Guo Dec 16 '19 at 4:21

There are several historical counting systems in Chinese, many of those use the same character to represent different values. Although there is a standard counting system today, the remnant 兆 causes confusion.

The character 兆 in mainland China refers to a million. However, 兆 in Taiwan refers to this number 1,000,000,000,000.

The reason I wrote out 1,000,000,000,000 is that interestingly, English has the same confusion, since there exist not only one counting system in English, namely "the long system" and "the short system". In "the long system", 1,000,000,000,000 is referred to as a "billion"; in "the short system", 1,000,000,000,000 is referred to as a "milliard". This discrepancy cause lots of transatlantic confusions.

In Chinese, , this confusion is easily avoidable. Since 万 means 10,000 and 亿 means 100,000,000 across all systems, 万亿 is no doubt 1,000,000,000,000.

According to Chinese (mainland) national standard, only the metric prefix "mega-" (for 106) is 兆, while a trillion (1012) should always be 万亿, never 兆.

e.g. 一兆字节 (or 一兆 for short) means one megabyte (1 MB), and 一兆赫 means one megahertz (1 MHz).

http://zjj.beijing.gov.cn/wsbs/infoview.asp?ViewID=50494

10的6次方 兆 M

10的4次方称为万，10的8次方称为亿，10的12次方称为万亿

In Taiwan, most people use 兆 for 1012.

zdic.net 　3. 数名，等于百万（古代指万亿）：兆周（电磁波频率单位，每秒一百万周的频率为一兆周）。

Nowadays, I hear not, many people write 兆, except when you want to express an extremely large amount.

• I've edited the question to correct the typo you mentioned. – fefe Apr 16 '18 at 0:21
• Sorry to trouble you, gf is somewhat pedantic! She complained. – Pedroski Apr 16 '18 at 2:41

Number over five digitals, namely beyond 萬, there are several ways of counting. 億兆京 has several interpretations. This causes discrepancy in meaning. In tradition, to avoid ambiguity, 萬萬, 十萬萬, 百萬萬, 千萬萬, 萬萬萬, 十萬萬萬... is used instead.

There are three interpretation of 一兆.

1. 一百萬 = 10⁶. Current it is found in some Chinese prefix of SI Units. 1 MHz = 一兆赫.
2. 一萬萬萬 = 10¹². Big numbers count in Hong Kong, Japan, South Korea and Taiwan.
3. 一萬萬萬萬 = 10¹⁶.

Mainland China:

91 2513 0522 6915 0159 = 91亿2513万522亿6915万159 (91亿亿)

1 MB = 1兆字节

Taiwan:

91 2513 0522 6915 0159 = 91京2513兆522亿6915万159

1 MB = 1百万字节