My textbook (みんなの日本語, 2e, TWnese edition by 大新書局) and teacher teach that いち/一 is added for powers of 10000 (ten thousand), but not for other powers of 10 (ten). (That's not exactly how they phrase it, but this is the generalization I'm extracting from what they state.)

numeral kana (pitch accent: ꜜ→) kanji English (citation form)
1 いち one
10 じゅꜜう ten
100 ひゃくꜜ hundred
1000 せꜜん thousand
1,0000 いちまꜜん 一万 ten thousand
10,0000 じゅうまꜜん 十万 hundred thousand
100,0000 ひゃくまꜜん 百万 million
1000,0000 せんまꜜんfn 千万 ten million
1,0000,0000 いちꜜおく 一億 hundred million

fn The textbook (p161) really shows せんまん (千万), not いっせんまん (一千万). Some users tell me that the latter is what people prefer.

I asked my teacher whether one can add いち/一 in the other cases (powers of 10 which are not powers of 10000), and he replied that, yes, sometimes people will say things like いっせん/一千 for clarity, such as when discussing money, perhaps in a store or for a bank check. My questions:

  • When exactly can 一 (いち/いっ/similar) be added before number-initial 十/百/千? (= When does it not sound wrong?)
  • When is it customarily added? (= When would or might people actually do this?)
  • What would be the pitch accent in those cases?

Here are some related questions, which don't address my point:

  • I'm confused about what you're asking about. Your linked answered seem to answer the question you've posted here. Perhaps you can explain what they've not answered. Otherwise, it looks like you've merely pointed out duplicates to your own question.
    – A.Ellett
    Commented May 26 at 15:06
  • The question about pitch accent would properly be better as its own separate question so as not to get muddled with tangential questions.
    – A.Ellett
    Commented May 26 at 15:07
  • @A.Ellett The other posts express uncertainty about what the general rule is and ask about what it is and about its rationale. My post assumes a specific rule as the default, doesn't ask about the rationale, and asks about specific exceptions. (Also: My post contains a really nice table :-P) Commented May 26 at 15:16
  • @A.Ellett I understand your point about pitch accent – but I don't yet know which patterns exist. (Is 一十 ever legal?) Also, in a sense, one can argue that pitch accent should be part of an answer, just like an IPA transcription might be part of an answer about an English word. I guess I could later ask a separate question, but: (1) let's first wait, and (2) the answers are probably simple. That said, I will accept answers as correct if they don't discuss pitch accent at all. Commented May 26 at 15:20
  • @A.Ellett As a linguist and hobby lexicographer I'm generally interested in majority usage (and in "significant minority" usage). In this case, I would like someone to put more meat on the statement by my teacher. Commented May 26 at 16:10

1 Answer 1


The situation is completely different for 10/100 and for 1000.

いちじゅう【LHLLL】 and いっぴゃく【LLHHH】 are jargon used only in special contexts, and laypeople never use it. When you do have a reason to use it, you may want to pronounce 2 as ふた, too. See my previous answer for details. Winning numbers of a lottery used to be announced like ふたせんいっぴゃくいちじゅうふた in the past, and this was when I learned something like いちじゅう is okay in special situations. However, this practice seems to have been discontinued, and they pronounce numbers simply like にせんひゃくじゅうに in this recent video. Again, this is a special convention in some industries, and many native speakers may not even know this.

1000 is tricky. It's almost always いっせん when it directly comes before まん for some reason. In other contexts, せん and いっせん【LLHL】 are both common and are basically interchangeable. In my experience, the default choice is せん in everyday shopping or such, but いっせん are often chosen in the following situations:

  • When numbers need to be conveyed accurately or digit-by-digit, such as on the phone or in math problems
  • When the number is precisely 1000 and saying only せん sounds a bit too short. For example, many people (unconsciously) read 1000m as いっせんメートル but 1100m as せんひゃくメートル.
  • Is [いっぴゃく]{LLHHH} heiban or odaka ([いっぴゃく(は)]{LLHHHLLL}), or would the distinction not make sense for this lexical item? Commented May 27 at 2:10
  • 2
    @LoverofStructure It's rarely followed by a particle, but my intuition says it's odaka...
    – naruto
    Commented May 27 at 2:23
  • Do laypeople not use いちじゅう and いっぴゃく for contrastive emphasis? I know that their equivalents are not uncommonly used that way in Chinese, for instance. “にじゅうさんですか?” — “違います、いちじゅうさんです!”. Commented May 27 at 7:58
  • @JanusBahsJacquet Most people never do that at all. I wouldn't be surprised if a few people come up with it after failing to convey the number many times, though.
    – naruto
    Commented May 27 at 8:31

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