Many things depend on this answer, so I'll offer you a guestimate. If your home is a single story, 2600 sq ft with 8 ft ceilings, and pretty loose leakage, you'll need approximately a minimum BTU/hr of 31200 BTU's, and a maximum of 62400 BTU's/hr. If it's a 2 story, with 8' ceilings, and average leakage, you'll want a minimum of 20280 BTU's and a maximum of 40560 BTU's/hr. Please check with your local professional to be exact.
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.
One ton per 1000 sq ft.
acdirect.com has a sizing chart- go to the site and determine the zone you live in... it's easy.
40,000 square feet
986,532,940,800 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
The size of the area that a portable air conditioner will keep cool varies depending upon the number of BTU's the unit has. For example, a 12000 BTU air conditioner will cool an area between about 500-600 square feet while a 8000 BTU air conditioner will cool an area of approximately 300-350 square feet.
Illinois comprises about 1.6 trillion square feet.(1,614,661,171,200 square feet)