I recently created a web app called Kazu which aims to help speakers of Japanese and English learn to read numbers in both languages.

I found a web page which said that 'for numbers over 1万, "1000" is read as いっせん.

So, to be consistent with 一千万{いっせんまん}, I used 一千億{いっせんおく} and 一千兆{いっせんちょう}.

I'm also using いっせん where 1000 appears in other parts of the number, so 1万1000 comes up as いちまん いっせん.

I've tried to clarify with 2 native speakers whether these are the best choice for the app, and both of them said "it depends on the person", but they also said せんおく sounds better than いっせんおく — except when there's a counter word like or .

Now I'm really confused. If you had to choose one "best" pronunciation for 1000億 and 1000兆, as in my situation, what would they be? What would you say for numbers like 1万1000? Should I change my decision?

  • possible duplicate of Prefixing `一` to numbers
    – istrasci
    Commented Mar 12, 2014 at 14:57
  • 2
    I searched before posting and found that thread, but it didn't have the answer of which numbers usually take いっせん.
    – sebu
    Commented Mar 12, 2014 at 22:03

2 Answers 2


This is mostly about "Names of Digits vs. Concrete Numbers" with some exceptions.

For instance, "10,000,000", as a digit (which is an abstract concept in math), is read either 「せんまん」 or 「いっせんまん」. Both are correct but more native speakers would say it 「せんまん」 for a digit at least in Tokyo and Nagoya. So we go like this:


As a concrete number, however, "10,000,000" can only be read 「いっせんまん」. That means that whenever a counter word is added to this, the 「いっ」 part must always remain.



Moving on, "1,1000", even as a concrete number, unfortunately has two readings. More formally, 「いちまんいっせん」 and less formally, 「いちまんせん」.

A store clerk or bank teller will say「いちまんいっせん円」 to a customer.

You look inside your wallet to check how much money you have and you will say to yourself 「いちまんせん円」. You say the same when telling your friend how much you have.

Thus, the best way to pronounce a number depends on the context, purpose, etc.

  • Excellent. Thanks very much — that's the kind of contextual explanation I was hoping for. It seems safer to go with いっせん my case, since it risks sounding merely unnatural as opposed to incorrect. I think I'll add an explanation of this usage you mentioned on the app. Thanks for going into detail!
    – sebu
    Commented Mar 13, 2014 at 2:13
  • 1
    I'm afraid that "digit" means something else: 10,000,000 is a number, (in base ten) written using one instance of the digit "1" and seven instances of the digit "0". I'm not sure what difference you're trying to capture, but "digit" is the wrong word. In English you can also say "a hundred" or "one hundred", but as far as I know, they are completely interchangeable.
    – Earthliŋ
    Commented Mar 13, 2014 at 7:27
  • 1
    @Earthliŋ, 「桁の名前」のことではと。
    – Yang Muye
    Commented Mar 13, 2014 at 9:25
  • @Tokyo Nagoya and Earthliŋ: There are a number of mathematical expressions with slightly different meanings. I think you want to say either: "10,000,000" is a whole number without units such as (the currency unit)yen or minutes. However if the same principle also applies to decimals such as "10,000,000.5" (or π (3.14...)) then I think you want to say it is a pure number without units.
    – Tim
    Commented Mar 13, 2014 at 11:15
  • BTW: I am always surprised how many text books fail to point out that where as larger English counters are in multiples of 3 zeros (ie 1 million = 1000 thousand), the large Japanese counters are in multiples of 4 zeros ("1万万"=1,0000,0000=1億;"1万億"=1,0000,0000,0000= 1兆). It makes them so much easier to remember.
    – Tim
    Commented Mar 13, 2014 at 11:30

I suppose 千億 is more abstract than the concrete number 一千億. As for your program, just follow the normal rule, that's enough. So,

1000億: いっせんおく
1000兆: いっせんちょう
1万1000: いちまんいっせん    

It's clear that different speakers have different preference to read 千. (数字の読み方)

By the way, I really like your app. Can you add アクセント{HLLLL} and the pronunciation the combination of numbers and [助数詞]{counters} as well? I wanted to create such an app many years ago, and gathered a lot of data. If you are interested, I will share them with you.

I saw you released the source under the MIT licence, are you hosting it on Git-hub?

  • Thanks for the advice & feedback. I'll consider adding アクセント and would be interested to see any data you'd like to share on that. I'm not sure how to go about counters though, since there are so many and it might make the app bloated. Maybe you have some ideas for that? And yes, it's on GitHub: github.com/sebpearce/kazu
    – sebu
    Commented Mar 13, 2014 at 1:15
  • Numbers aren't that difficult to learn, you just have to remember 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 100, 1000, 10,000, 100,000,000, 1,000,000,000,000, etc. As it stands, the app only serves to help learn these fifteen numbers and eight exceptions, which are 300, 600, 800, 1000, 3000, 8000, 100,000,000 and 1,000,000,000. Adding counters, the app might be of value not only to complete beginners, but to learners at practically all stages.
    – Earthliŋ
    Commented Mar 13, 2014 at 8:02
  • @Earthliŋ I created the app firstly to help myself, and I'm around a B2 level. I still have trouble with the numbers in between the groupings of 万, 億 and 兆. Quick, what's 2 billion in Japanese? What's 75 million? It's not as easy as memorizing the numbers you listed. So I disagree that it's only of value to complete beginners. I got a message from a professional English-Japanese translator the other day saying he'd been waiting forever to get something like this, because he still has trouble with numbers. That said, I'm still considering the counter idea.
    – sebu
    Commented Mar 15, 2014 at 5:14

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