Most Air Conditioning Suppliers on the internet have a different method of estimating air conditioner size requirements. At the end of the day it's going to be an estimate at best.
Assuming a 3 Metre Ceiling, that makes 260 x 3 = cubic metres 780 cubic metres.
If there was no heat gain at all then you'd probably go for about 300 BTU per cubic metre if it has south facing windows, or 200 per cubic metre if not. So this room would be starting at 234,000 BTU for south facing windows, or 156,000 BTU if there are none.
For heat gain, they say add 400 BTU for each person or heat generating piece of equipment too.
All in all, it's a pretty huge area to air condition, the expense and power requirements are going to be massive. If it's a house then it's probably sensible to just air condition the rooms which need air conditioning with seperate portables or fixed installs. If it's a big commercial or industrial area then evaporative cooling or fans might be a more realistic proposition.
3 ton
Yes, a 4.5 ton air conditioner would be the minimum size for 2000 square feet.
about 75000 btu
Depends where you live, the old rule of thumb is 500 square feet for 1 ton.
It depends on your location, shade, windows, and insulation. You should be able to find a local A/C contractor who will do what's called a J-load calculation. There are also online calculators that will give you a rough approximation if you have an idea of how good your insulation and windows are.
One ton per 1000 sq ft.
4 Ton
acdirect.com has a sizing chart- go to the site and determine the zone you live in... it's easy.
986,532,940,800 square feet.
40,000 square feet
It depends on the climate, insulation, and layout of the room. In general, a 1 ton air conditioner is suitable for a room between 400-800 square feet, so it may struggle to adequately cool a room of 1800 square feet. It is recommended to use a larger capacity air conditioner for a room of that size.
If it's a square room then the room size is 14 feet by 14 feet