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ken (6 shaku, approx. 1.818 m)
counter used to number the gaps between pillars
「間」 has other readings with different meanings.
この部屋は六畳半二間です。
This room is 6.5 tatami by 2 ken.
家の奥行きは三間あります。
The house is 3 ken deep.
二間幅の広い廊下を歩きました。
I walked down the 2-ken wide corridor.