Meaning
階 covers three related ideas: floor or story of a building, staircase or steps, and rank, grade, or level. Day to day, you will meet it most often on elevator panels and building directories — 一階 (ground floor), 二階 (second floor), and so on. It also builds the word 階段 (staircase), which comes up constantly in Japan.
Break the character into its two parts. On the left is 阝, a compressed form of 阜 (an earthen mound) — a radical that keeps company with kanji connected to terrain and elevation. On the right is 皆 (みな / カイ), meaning "all" or "everyone," whose role here is mostly phonetic, lending 階 its カイ reading. Picture stone steps cut into a hillside, everyone (皆) ascending level by level (阝). That image runs through every meaning of the character.
Japanese school children learn 階 in Grade 3, around age 8–9. It has 12 strokes and uses the radical 阝(こざとへん) — the "small mound" on the left. Don't confuse it with ⻏(おおざと), a look-alike that sits on the right side of other kanji. Past the literal floors and stairs, 階 reaches into abstract territory: social class, military rank, and musical scale all use compounds built on this character.
Readings
On'yomi (音読み) — Chinese-derived readings
カイ is the dominant reading and shows up in nearly every compound. It entered Japanese via Middle Chinese and works equally across formal, academic, and everyday vocabulary.
- 階段 (kaidan) — staircase, stairs. The most common everyday compound.
- 階級 (kaikyuu) — class, rank, social stratum. Used in social and military contexts.
- 階層 (kaisou) — hierarchy, layer, stratum. Appears in social science and computing alike.
- 段階 (dankai) — stage, phase, step in a process. A staple of business and academic Japanese.
- 音階 (onkai) — musical scale (literally "sound steps"). Used in music education.
Kun'yomi (訓読み) — Native Japanese readings
The kun'yomi is きざはし, but you won't hear it in modern speech. It belongs to classical poetry, old chronicles, and formal descriptions of shrine or palace architecture. The word conjures a specific image: stone steps rising toward something grand.
- 階 (kizahashi) — stone steps, a flight of stairs (literary/classical usage).
Common Words & Compounds
階 appears constantly in speech about buildings, so its compounds are practical to learn. Here they are by theme.
Building Floors:
- 一階 (ikkai) — first floor, ground floor
- 二階 (nikai) — second floor
- 三階 (sangai) — third floor
- 地下階 (chika-kai) — basement floor, underground floor
- 上階 (joukai) — upper floor(s)
- 下階 (gekai) — lower floor(s)
- 最上階 (saijoukai) — top floor, uppermost floor
Stairs & Steps:
- 階段 (kaidan) — staircase, stairs
- 階段室 (kaidan-shitsu) — stairwell
Rank, Level & Hierarchy:
- 階級 (kaikyuu) — class, rank, grade (social or military)
- 階層 (kaisou) — hierarchy, stratum, social layer
- 段階 (dankai) — stage, phase, step (in a process)
- 位階 (ikai) — court rank, imperial rank
Other:
- 音階 (onkai) — musical scale
Example Sentences
エレベーターが故障しているので、階段を使ってください。
Erebeetaa ga koshou shite iru node, kaidan wo tsukatte kudasai.
The elevator is broken, so please use the stairs.
図書館は三階にあります。
Toshokan wa sangai ni arimasu.
The library is on the third floor.
この建物は何階まであるんですか？
Kono tatemono wa nankai made arun desu ka?
How many floors does this building have?
彼女の部屋は二階の一番おくにあります。
Kanojo no heya wa nikai no ichiban oku ni arimasu.
Her room is at the far end of the second floor.
プロジェクトは次の段階に進みました。
Purojekuto wa tsugi no dankai ni susumimashita.
The project has moved on to the next stage.
彼は軍の階級で大佐です。
Kare wa gun no kaikyuu de taisa desu.
He holds the military rank of colonel.
最上階からの景色はとても美しかった。
Saijoukai kara no keshiki wa totemo utsukushikatta.
The view from the top floor was absolutely beautiful.
ピアノを習い始めたばかりなので、まず音階の練習をしています。
Piano wo narai hajimeta bakari na node, mazu onkai no renshuu wo shite imasu.
Since I just started learning piano, I'm practicing musical scales first.
この社会には複雑な階層が存在する。
Kono shakai ni wa fukuzatsu na kaisou ga sonzai suru.
Complex social strata exist in this society.
Memory Tip
Picture a grand earthen hill (阝) with everyone (皆) climbing up in single file, each person on a different step. Floors, stairs, social rank — 階 runs through all of them because the core idea never changes: moving between levels. Spot 阝 on the left of a kanji and you are usually dealing with terrain, height, or ascent.