Problems with UU and metres

So I’ve read that 1 UU equals 1cm I made my grid to show 100 that would be 1 metre. Scaled the floor to 22.3 x 22.4 to get approx. 500m2 I’ve placed walls and tried making a room but placing chairs seems to swallow up 1 metre per chair. When I press play everything feels too small. How do I do this if I want to make architecture?

This is supposed to be 4 metres the chair is supposed to be 80cm but looks like a 40cm chair.

This room is 14 Meters long I’m using a standard chair with 42x47UU it fits in about 24 times. I can fit a chair like that 24 times in 11 metrs. The UU to CM seems messed up. 1 UU is not 1 cm