# All the ways of writing numbers

I couldn't find any sites where I could get a comprehensive list of possible number writing formats. My question is mainly about mixing and matching different ideas I've seen online.

For general, whole numbers, which of these are possible:

１２３万３４５

１２３３４５

For rationals, the only real question I have is if you can mix decimal fractions with whole numbers like so: 百二点一厘 for 102.01, or if you need to do it like 百二点〇一 or anything similar.

You can get a good overview from the government's official guideline 公用文作成の考え方 (see Annex I-4), which was just revised this year, though it is not the only decisive rules.

In general, there are several modes of consistent styles for horizontal and vertical writings respectively, and mixing conventions from multiple systems is not a recommended practice.

1. For horizontal writing

1. Positional notation, Western-style separators

123,045,067.089

2. Positional notation, Japanese separators

1億2304万5067.089

Note 1: Japanese fractional units (割, 分, 厘……) are not to be used together with most of dimensionless units larger than 1.

Note 2: there sometimes seen thousand-based delimiting in statistic or financial fields to align with Western ledger sheets.

123百万045千067.089

3. Spelled out

一億二千三百四万五千六十七点〇八九 or
一億二千三百四万五千六十七・〇八九

4. (bonus) Anti-forgery spelling for accounting (大字)

壱億弐阡参陌肆萬伍阡陸拾漆円
壱億弐千参百四万五千六拾七円 (legal style)
etc.

2. For vertical writing

1. Positional notation, Western-style separators

一二三、〇四五、〇六七・〇八九

However, for numbers in fixed formats and/or of small amount (e.g. dates, ID, percentage...), Arabic numerals are also used. Such lesser digit numbers are often packed into one character size in professional typesetting (縦中横). See:

2. Positional notation, Japanese separators

一億二三〇四万五〇六七・〇八九

3. Spelled out
(same as 1-3)

4. Anti-forgery spelling
(same as 1-4)

The fullwidth vs. halfwidth Arabic numeral usage is a highly controversial topic with much disagreement across house rules, but unless you are a typesetter, sticking to halfwidth figures seems the best practice.

There are a lot of rules around this, but basically:

• You use 万, 億, 兆, etc. but not 千, 百, 十. So 一二三三四五 is not used and 百2十3万３百４十５ is not acceptable.
• Use commas: １２３３４５ should be 123,345.

If the text is horizontal, １２３万３４５ should be fine but the number is small enough to use "123,345". If it gets bigger, use of 億 or 兆 is necessary. If the text is vertical 一二三万三四五 may be used but 百二十三万三百四十五 would be more common (contrary to the first rule above).

For decimals, in most horizontal texts, only Arabic numerals are used. In vertical texts, ５・０８ or 五・〇八 is used to mean 5.08. Notation like 3割2分 or 三割二分 is used mostly in specific contexts such as statistics related to some sports.

I think style guides like this contain a lot more details.