I didn't know there were such calculators. Are they some sort of sales gimmick?
I would say the best way to find out what room treatment your room needs is to consult an expert. GIK Acoustics and RealTraps should be able to help - my experience is with GIK and they will give you free advice in the hope that you buy their products.
http://www.gikacoustics.com/products/http://realtraps.com/There's plenty of good advice on both sites.
In simple terms there are Bass Traps, that even out the bass frequencies (the biggest issue with small rooms), other absorption panels to deal with wall and ceiling reflections, and diffusion, which keeps sound energy in the room by spreading it about.