floor; storey
Refers to a level or storey of a building. Often used as a suffix after a number or descriptor, e.g. 二階 (second floor).
このビルは五階建てです。
This building is five storeys tall.
受付は二階にあります。
The reception desk is on the second floor.
Rare standalone noun for stairs; the reading きざはし is more common for this meaning. Modern Japanese usually uses 階段 (かいだん).
See also: 階 (きざはし)
古い文献では「階」を「きざはし」と読んで階段を指すことがある。
In old texts, 階 can be read as きざはし and refer to stairs.
Technical term in chronostratigraphy for a stage, a unit of geological time. Not used in everyday conversation.
この化石は白亜紀のアルビアン階のものです。
This fossil is from the Albian stage of the Cretaceous period.
counter for floors
Counter used for storeys or floors of a building. Attaches to numbers: 一階 (first floor), 何階 (which floor?).
このデパートは地下二階から八階まである。
This department store has floors from the second basement to the eighth floor.
This apartment building has ten floors.
I went up to the fifth floor by elevator.
The bookstore is on the third floor of the department store.
Excuse me, what floor is the restroom on?
階 is the everyday counter for a building's floors (三階 = third floor), while 層 as a counter is a more formal or technical term often used in architectural or structural descriptions.
hierarchy; stratum; layer; level; class
top floor; uppermost floor
musical scale
upper floor; upstairs · top of the stairs
lower floor; downstairs · bottom of the stairs; foot of the stairs
each floor; every floor
number of floors; number of stairs · rank; order
court rank; official rank
first floor; ground floor · one floor; one storey · one rank
third floor; third storey
second floor; upstairs
what floor; which floor
upper floor; floor above; upstairs
floor below; lower floor
monastic rank; rank of a monk
ordination
Shinto divine rank; rank of Shinto gods
job ranking; job grade; occupational rank