# Calculating cooling power for server room

I'm trying to calculate how much cooling power I need to keep a server room (about $$60 m^2$$ with $$3m$$ height) in 25℃.

How exactly I should do this calculation?
I summed up wattage of all equipments and converted it to BTU/h.

1. is this correct? do devices make heat as much as their wattage (at maximum of-course)?

Now How can I select Air conditioner for this room?
I think extracting 300 btu/h in a $$10m^3$$ differs from extracting same BTU/h in a $$100m^3$$

1. How to decide how many air conditioners do I need?

can you please explain calculations needed for a general cooling problem?