Ezekiel 40:6-7

6Then he went to the gate on the east side. He climbed its steps and he measured the size of the entrance. It was 3 metres deep.

7Beyond this was a passage with three rooms on each side. They were rooms for the guards. Each of these rooms was 3 metres long and 3 metres wide. The walls between the rooms were 2½ metres thick. Beyond them was a passage that was 3 metres long. This went to an entrance room to the yard of the temple.