Translation guide
The English idiom 'piece of cake' means something is very easy. In Japanese, there are several natural ways to express this, ranging from casual idioms to straightforward statements.
To say that something is extremely easy or simple to do.
Do not translate 'piece of cake' literally as ケーキの一片 (a slice of cake). It will not be understood as an idiom.
A common idiomatic expression meaning 'a piece of cake' or 'a breeze'. Literally 'before breakfast', implying the task is so easy you can do it before eating.
This is a piece of cake.
A playful, somewhat old-fashioned idiom meaning 'a piece of cake'. Often used in a lighthearted way.
That job is a piece of cake.
Means 'easy victory' or 'a walk in the park'. Used when something is effortlessly easy.
The exam was a piece of cake.
The most straightforward word for 'easy' or 'simple'. Not an idiom, but perfectly natural.
That's a piece of cake.
Means 'with ease' or 'no sweat'. Often used by younger speakers.
I beat that game, piece of cake.