which is which

Phrase

as a question especially informal

(informal, especially as a question) Used to indicate multiple things are difficult to tell apart

Japanese Meaning

対象が複数存在して、それぞれの違いが識別しにくい状態。 / どれがどれなのか分からない状態を示すフレーズ。

After painting both jackets the same, I couldn't tell which is which.

両方のジャケットを同じように塗ってしまって、どれがどれだか区別がつかなかった。

Sense（1）

(informal, especially as a question) Used to indicate multiple things are difficult to tell apart