Large Numbers: 万, 億, 兆 (Grouping by Four)

Large numbers are the one part of the Japanese counting system that genuinely defeats otherwise-fluent English speakers — not because the words are hard, but because the two languages chop the digits into different-sized pieces. English groups by thousands (that's what the commas in 1,000,000 mean: thousand, million, billion — a new word every three zeros). Japanese groups by ten-thousands: a new place-word every four zeros. Once you see that a Japanese number is comma'd 1,0000 rather than 10,000, everything clicks — and there's a mechanical trick to convert on the fly. This page teaches the four-digit system and the trick.

The three big place-words

Above the ordinary numbers you already know sit three myriad-based units, each four zeros bigger than the last:

The crucial thing to internalize: each of these is 10,000 times the one below it, not 1,000 times. 万 × 10,000 = 億; 億 × 10,000 = 兆. That constant factor of ten-thousand is the whole system. English's units (thousand → million → billion) each multiply by only 1,000, which is exactly why the two systems keep drifting out of alignment as the numbers grow.

Everything between the place-words is an ordinary 1–9999

Here's the mechanism. Between one place-word and the next, you write a perfectly ordinary number from 1 to 9,999 — the same numbers you already build with 千, 百, 十. That number tells you "how many 万" or "how many 億" you have.

So to name a number, you break it into four-digit chunks from the right, and label each chunk:

Each chunk is a normal 1–9,999 number; the place-word (万 / 億 / 兆) after it tells you which four-zero band it sits in. Read them left to right, biggest band first.

Building 100,000 and 1,000,000 — where English speakers stumble

English has no single word for "ten thousand," so English speakers instinctively want a new word at 100,000 and 1,000,000. Japanese doesn't give them one — those numbers are just multiples of 万.

• 100,000 = ten ten-thousands = 十万 jū-man. (Not a new word — literally "10 × 10,000.")
• 1,000,000 = a hundred ten-thousands = 百万 hyaku-man. (This is the English "million.")
• 10,000,000 = a thousand ten-thousands = 千万 sen-man.
• 100,000,000 = ten million ten-thousands would overflow 万, so a new word appears: 一億 ichi-oku.

The comma trick: re-group by fours

Here is the conversion method that competing explanations skip. English writes big numbers with commas every three digits, which is optimized for English's thousand-based words. To read the number the Japanese way, re-comma it every four digits from the right and read off the place-words.

Take 1,200,000 (one point two million). Strip the English commas and re-group by four from the right:

1200000 → 120,0000

Now the rightmost group is the ones-through-9999 chunk (0000 = nothing), and the next group up is the 万 band: 120 万 = 百二十万 hyaku-ni-jū-man. Done. The number that looked like "1.2 million" is hyaku-ni-jū-man, "120 ten-thousands."

One more: 35,000,000 (thirty-five million).

35000000 → 3500,0000 → 3,500 in the 万 band → 三千五百万 san-zen-go-hyaku-man.

Notice 千四百万 sen-yon-hyaku-man (14,000,000): the chunk before 万 is the ordinary number 千四百 (1,400), so it reads "1,400 ten-thousands" = 14 million. Re-comma'd by fours, 14,000,000 becomes 1400,0000 — and 1,400 in the 万 band is exactly what you say.

億 and 兆 in the wild

You meet 億 constantly in the real world: populations, company valuations, national statistics. Japan's own population is the textbook case.

一億二千万 ichi-oku-ni-sen-man breaks into two labelled chunks: 一億 (1 in the 億 band = 100,000,000) plus 二千万 (2,000 in the 万 band = 20,000,000), totalling 120,000,000. Read biggest band first, and each band is a normal number.

兆 chō (a trillion) shows up mainly in economics and national budgets. Note its sound change with 一: 一兆 is いっちょう itchō, not ichi-chō — the same gemination you see in counters (covered on Sound Changes in Numbers).

Why the mismatch feels so hard — and why it isn't

The difficulty is purely one of regrouping, not of new vocabulary. English "million / billion / trillion" land at 10⁶, 10⁹, 10¹² — every three zeros. Japanese 万 / 億 / 兆 land at 10⁴, 10⁸, 10¹² — every four zeros. They only coincide again at 兆 = trillion = 10¹². In between, the words interleave awkwardly:

Study that table until the pattern is muscle memory: the Japanese column advances to a new word one row later than English does (万 covers three English rows), which is exactly the four-versus-three grouping made visible. Don't fight it by translating word-for-word; regroup the digits by four and read off the bands.

Common mistakes

English speakers reach for a single "million" word or try to double up 千. A million is a hundred ten-thousands: 百万.

The most common decoding error is being off by a factor of ten or a hundred. 億 is 10⁸ (a hundred million), so 十億 is 10⁹ — a billion. Re-comma by fours and count bands to avoid the slip.

A digit-plus-place-word is always a multiplication: 百万 is "a hundred ten-thousands," 1,000,000 — not "a hundred and a ten-thousand." Big-place-word means multiply.

Just like counters, 一 tightens before 兆: itchō, not ichi-chō. Watch for the same gemination in 一億 → ichi-oku stays clean, but 一兆 → itchō doubles.

Key takeaways

• Japanese groups large numbers in fours: 万 (10⁴), 億 (10⁸), 兆 (10¹²) — each ten-thousand times the last.
• Between place-words sits an ordinary 1–9,999 number telling you how many 万 / 億 / 兆 you have.
• Anchor conversions: million = 百万, billion = 十億, trillion = 一兆 (itchō).
• The trick: re-comma the digits every four from the right, then read off the bands (1,200,000 → 120,0000 → 百二十万).
• Read biggest band first; a digit before a place-word always multiplies it.