Japanese has two extremely common counters that both sound like "kai": 階（かい）, which counts the floors of a building, and 回（かい）, which counts times or occurrences. Written, they are different kanji and cause no confusion. Spoken, they are so close that learners constantly mix up their readings — and the mix-up matters, because at the number 3 the two counters split apart: 三階 is さんがい (sangai) but 三回 is さんかい (sankai). This page teaches both together, so you drill the near-minimal pair exactly where it counts.
〜階: floors of a building
階 counts the storeys of a building. The first floor / ground floor is 一階 (ikkai), and Japanese counts up from there in the American style — so a building's "second floor" (二階) really is one flight up, not two. The kanji 階 also means "steps/rank," which fits: a floor is a level in a stack.
トイレは一階にあります。
toire wa ikkai ni arimasu
The restroom is on the ground floor.
受付は三階です。エレベーターをご利用ください。
uketsuke wa sangai desu. erebētā o goriyō kudasai
Reception is on the third floor. Please use the elevator.
オフィスは先月、六階に引っ越しました。
ofisu wa sengetsu, rokkai ni hikkoshimashita
The office moved up to the sixth floor last month.
The readings of 階 — and the がい variation
階 begins with k, so it geminates after 一, 六, 八, 十 (ikkai, rokkai, hakkai, jukkai) and — this is the distinctive part — it voices to がい (gai) after ん, in 三階 and 何階.
| Number | Reading | Note |
|---|---|---|
| 一階 | いっかい (ikkai) | gemination |
| 二階 | にかい (ni-kai) | — regular |
| 三階 | さんがい (sangai) | voicing k → g after ん |
| 四階 | よんかい (yon-kai) | — regular |
| 五階 | ごかい (go-kai) | — regular |
| 六階 | ろっかい (rokkai) | gemination |
| 七階 | ななかい (nana-kai) | — regular |
| 八階 | はっかい / はちかい (hakkai / hachi-kai) | gemination optional |
| 九階 | きゅうかい (kyū-kai) | — regular |
| 十階 | じゅっかい / じっかい (jukkai / jikkai) | gemination |
| 何階 | なんがい (nangai) | voicing k → g after ん |
Related 階 patterns: 〜階建て and 地下
Two everyday extensions ride on 階. 〜階建て（かいだて） describes how many storeys a building has: 三階建て (sangai-date) = "three-storey." And basement floors use 地下（ちか） plus 階: 地下一階 (chika-ikkai) = "the first basement level (B1)."
実家は三階建ての一軒家です。
jikka wa sangai-date no ikkenya desu
My parents' place is a three-storey detached house.
食料品売り場は地下一階です。
shokuryōhin uriba wa chika-ikkai desu
The grocery floor is one level down, on B1.
〜回: times and occurrences
回 counts repetitions — how many times something happens. It pairs naturally with frequency expressions (週に〜回 "per week," 一日に〜回 "per day") and with any repeatable action.
この薬は一日に三回、食後に飲んでください。
kono kusuri wa ichinichi ni sankai, shokugo ni nonde kudasai
Take this medicine three times a day, after meals.
週に二回ジムに通っている。
shū ni nikai jimu ni kayotte iru
I go to the gym twice a week.
この映画、もう何回も見てるよ。
kono eiga, mō nankai mo miteru yo
I've already seen this movie so many times.
The readings of 回 — the same k, but no voicing
回 also begins with k and geminates identically (ikkai, rokkai, hakkai, jukkai). The one and only difference from 階 is that 回 does not voice after ん: 三回 stays さんかい (sankai), and 何回 stays なんかい (nankai).
| Number | 回 (times) | vs. 階 (floors) |
|---|---|---|
| 1 | いっかい ikkai | いっかい ikkai (identical) |
| 3 | さんかい sankai | さんがい sangai |
| 6 | ろっかい rokkai | ろっかい rokkai (identical) |
| What? | なんかい nankai | なんがい nangai |
このビルは三階まで吹き抜けになっている。
kono biru wa sangai made fukinuke ni natte iru
This building has an atrium open up to the third floor.
漢字は三回書けば覚えられる。
kanji wa sankai kakeba oboerareru
You can memorize a kanji by writing it three times.
Read those two aloud back to back: sangai (floor) then sankai (times). That single voiced-vs-unvoiced g/k is the whole game.
回 + 目: making ordinals
回 combines with 目（め） to turn a count into an ordinal — "the Nth time." 一回目 (ikkai-me) = "the first time," 三回目 (sankai-me) = "the third time." Crucially, 回目 keeps the unvoiced kai — it is 三回目 sankai-me, never sangai-me — because the underlying counter is 回, not 階.
日本に来るのは、今回で三回目です。
nihon ni kuru no wa, konkai de sankai-me desu
This is my third time coming to Japan.
一回目の受験は失敗したが、二回目で合格した。
ikkai-me no juken wa shippai shita ga, nikai-me de gōkaku shita
I failed the exam the first time but passed on the second.
For the ordinal system in general — 〜番目, 第〜, and friends — see Ordinal Numbers. For the other "times" counter, 度, and exactly how it differs from 回, see 〜度 (Times, Degrees, Temperature).
Common mistakes
❌ 三階 ＝ さんかい
Incorrect — the floor counter voices after ん: さんがい (standard).
✅ 三階 ＝ さんがい
sangai
third floor
❌ 三回 ＝ さんがい
Incorrect — the 'times' counter does NOT voice; it stays さんかい.
✅ 三回 ＝ さんかい
sankai
three times
The two errors above are mirror images — and they are the whole reason to learn these counters side by side. Floors voice (sangai); times don't (sankai).
❌ 何回 ＝ なんがい
Incorrect — 何回 (how many times) keeps the unvoiced kai: なんかい.
✅ 何回 ＝ なんかい
nankai
how many times
❌ 一階 ＝ いちかい
Incorrect — 階 geminates after 一.
✅ 一階 ＝ いっかい
ikkai
ground / first floor
❌ 三回目 ＝ さんがいめ
Incorrect — the ordinal rides on 回 (kai), not 階; it's さんかいめ.
✅ 三回目 ＝ さんかいめ
sankai-me
the third time
Key takeaways
- 階（かい） counts building floors; 回（かい） counts times/occurrences.
- Both geminate identically at 1, 6, 8, 10 (ikkai, rokkai, hakkai, jukkai).
- They split at 3 and "what?": floors voice (三階 sangai, 何階 nangai); times don't (三回 sankai, 何回 nankai). Standard prescribes the voiced floor forms.
- 一階 and 一回 are homophones (いっかい) — only context disambiguates.
- 回 + 目 makes ordinals — 三回目 sankai-me, "the third time," keeping the unvoiced kai.
Now practice Japanese
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Start learning Japanese→Related Topics
- 〜度: Times, Degrees, TemperatureN4 — The counter 度 (ど) for occasions, temperature, and angles — plus the subtle 回/度 split for 'times' and the everyday ambiguity of 今度 ('this time' or 'next time').
- Ordinal Numbers (番目, 第)N4 — How Japanese turns cardinal numbers into 'first, second, third' — the everyday 〜番目, the formal prefix 第〜, and the productive 〜目 suffix that ordinalizes any counter.
- Counter Sound Changes: The Master PatternN4 — The two euphonic rules behind nearly all counter irregularity — gemination after 一/六/八/十 and voicing after 三/何 — laid out as one master grid across 本, 匹, 分, 階, 冊, and 杯.