standing room 
noun [mass noun]
Space available for people to stand rather than sit in a passenger vehicle or building: the stadium has standing room for 12,000 supporters it is standing room only in this small bar...
- With the building full to standing room only as he delivers his spiel, there is a definite air of sanctity and reverence.
- We frequently hear that during rush hour many passengers are left with standing room only.
- He soon had the assembled crowds dancing and swaying on whatever standing room was available.