You know you're in a small dojo when:
-You bow before entering the dojo not because of etiquette but because there simply isn't enough room inside to stand upstraight.
-Horse-stance isn't an exercise but a necessity.
-In order to save space, the kamiza and the weapons-racks are just painted on the walls.
-If the dojo's walls weren't insulated, the room would be 25% bigger.
-When the sensei chose a calligraphy to adorn the kamiza, the main criterium he was concerned with was the thickness of the paper it was painted on.
-Prior to working on throws, you've been taught how to breakfall on a vertical
-When doing kata, table-knives are used as training substitutes for swords.
-When doing kata, chopsticks are used as training substitutes for staves.
-There's only one place in the dojo where you can practice the kiri-otoshi cut, that's the place where a slit has been made in the ceiling for that purpose.
-For the final salute, the students and the sensei don't bow at the same time lest they would hit each other's head.
Can't beat Oldman, but here's a picture of a dojo where I used to train three years ago. I think that was a pretty small dojo.