Counting in Japanese: Why 一本 Is いっぽん and 三本 Is さんぼん
You learned the counter 本 (ほん) for long objects, then heard いっぽん, さんぼん, ろっぽん and wondered if you misheard. You didn’t. Counters change their sound depending on the number in front, and there is a clear pattern behind it.
Why Counters Change Sound
When certain numbers meet certain counters, the sounds blend for easier pronunciation. The number may add a small っ, or the counter's first consonant may become voiced or half-voiced (は→ば→ぱ). It feels chaotic at first, but the same numbers cause changes again and again.
本 — counting long, thin objects
匹 (animals) and 回 (times)
匹 (ひき)
回 (かい)
It Depends on the Consonant, Not the Counter
Most textbooks give you a grid per counter and leave you to memorise each one separately. That is why counters feel endless. In fact the behaviour is decided almost entirely by the first consonant of the counter, so once you know which family a counter belongs to, you can predict it without ever having seen it.
The reason is physical. Saying いち + ほん quickly forces the tongue to cut the vowel short and hit the following consonant harder, which is what the small っ writes down. A consonant that is already hard to voice after that break turns into a p-sound. Nobody decided this. It is what the mouth does at speed.
| Counter family | Examples | After 1 / 6 / 8 / 10 | After 3 | Sounds like |
|---|---|---|---|---|
| は行 (h/f) | 本 ほん · 匹 ひき · 杯 はい · 分 ふん | small っ + p-sound | voiced to b | いっぽん · さんぼん · ろっぽん |
| か行 (k) | 回 かい · 階 かい · 個 こ · 件 けん | small っ, no voicing | usually unchanged | いっかい · さんかい · ろっかい |
| さ行 (s) | 冊 さつ · 歳 さい | small っ, no voicing | unchanged | いっさつ · さんさつ · はっさつ |
| その他 (m/n/d/r) | 枚 まい · 台 だい · 人 にん · 度 ど | no change | no change | いちまい · さんまい · ろくまい |
分 — the counter you will need most
Drill 分 (minutes) before any other counter. It runs right through the listening section: train times, appointment times, how long something takes. It belongs to the は行 family, so it behaves exactly like 本.
Watch 四分 (よんぷん) and 九分 (きゅうふん). Students who reach for し and く here get blank looks. Also note that 十分 is じゅっぷん for ten minutes but じゅうぶん when it means “enough”. Same two kanji, different word.
Counters That Never Change
Counters beginning with m, d, n or r do not change at all. One to ten, no exceptions. Learn these early; they cost you nothing.
いちまい · にまい · さんまい · よんまい
いちだい · にだい · さんだい
いちど · にど · さんど
人 (people) is a partial exception: 一人 (ひとり) and 二人 (ふたり) are irregular, but from three onwards it is completely regular: さんにん, よにん, ごにん. Note 四人 is よにん, not よんにん.
三回 and 三階 — same sound, different answer
Both counters are written かい and both begin with k, so you would expect them to behave identically. They do not.
三回
さんかい
three times, no voicing
三階
さんがい
third floor, voiced to が
The voicing in さんがい follows a wider habit: a sound after ん tends to voice, which is why you also get さんばい (三杯) and さんぜん (三千). 三回 resisted it, probably to stay distinct from 三階. One caveat: さんかい for 三階 is now common too, especially among younger speakers, so do not correct anyone who says it.
The 4, 7 and 9 Problem
Three numbers have two readings each, and choosing the wrong one is more noticeable than getting a sound change wrong.
- 4: よん is the safe default with counters (よんほん, よんまい). し appears in fixed words like 四月 (しがつ).
- 7: なな is the safe default (ななほん). しち survives in 七月 (しちがつ) and 七時 (しちじ).
- 9: きゅう is the safe default (きゅうほん). く appears in 九月 (くがつ) and 九時 (くじ).
There is a logic to it. Dates and clock times kept the older readings; everyday counting moved to the newer ones. With a counter, よん, なな and きゅう are the safe defaults.
Where This Appears on the JLPT
Counters are almost never a grammar question. They show up in listening, where someone says ろっぽん or さんがい once and the answer hangs on your catching it. Recognising the word on paper is a different skill. Reading this article will not give you the other one.
So say them out loud. Every year I have students who can pick いっぽん out of a written list and still miss it at speed, because they have never once made the sound themselves. Count the things around you in Japanese for five minutes. It beats an hour of staring at a grid.
The Pattern
- 1, 6, 8, 10 usually trigger a small っ: いっぽん, ろっぽん, はっぽん, じゅっぽん.
- 3 voices は行 counters: さんぼん, さんびき, さんばい (ほん→ぼん, ひき→びき, はい→ばい).
- 2, 4, 5, 7, 9 are usually regular: にほん, よんほん, ごほん.
- m, d, n, r counters (枚, 台, 度) never change at all.
- Exceptions cluster on common words, and 三階 さんがい is the one to know.
Teacher's Note
Don't memorize a giant grid. Learn the 1-6-8-10 → small っ and 3 → voiced shortcuts, practice 本 out loud until it's automatic, and the same instinct transfers to 匹, 回, 杯, 階 and the rest.
Count out loud, every day
Nihongo Pass drills counters with native audio so いっぽん and さんぼん come without hesitation.