Try it out:
GitHub link:

EDIT (2014-03-08): I’ve done a complete revision of the design and features. Have a look!

I wrote this little app in my spartan basement suite apartment in Vancouver in autumn 2013.

It’s a tool to help people who are learning Japanese. Large numbers in Japanese are a pain for English-speakers (and vice-versa) because they’re grouped in 4s, not 3s — but only after you get above 1,000.

  • sen = 1,000 (103)
  • man = 10,000 (104)
  • oku = 100,000,000 (108)
  • chou = 1,000,000,000,000 (1012)

Compare this to our units of thousand, million and billion.

  • English: 100,000 (a hundred thousand)
  • Japanese: 10万 = 10,0000 (ten man)

Since I kept getting these wrong, I wrote an app to help. You can experiment by generating random numbers or typing in your own and seeing what they look like in Japanese.

Try it here.