Hola, I think that you have a mistake in the measure of the plate, 6mm is very small.Well, supose that the plate is of 6 cm of diameter => 3.14x3x3= 28cm2. 6m2= 60000cm2, 60000/28=2.143 times the surface of a plate in the total room surface. 16colonies x 2143= 34,288 col in 6 m2 5714cfu/m2 57.1/dm2 0.571/cm2.
If the plate was different repeat he same procedure. Good luck
CFU/ cm2 is the number of colonies formed per cm2 of surface, so first work out the surface area of your plate.
I will assume you meant 6cm diameter plate rather than 6mm diameter, as 6mm is very small.
Area=pi*radius2
radius is 1/2 of the diameter, so pi*32 which is about 28cm2
if you had 16 colonies on that, then the CFU is 16 colonies per 28cm2
CFU/cm2 would me 16/28 = 0.57CFU/cm2
I am not sure what the size of the room has to do with anything, but I suppose you could calculate the total number of CFU in the whole room if you wanted to.