Calculating the need for air conditioning in the room

The need for the capacity of the air conditioner most certainly determine how big the room is that the air conditioner will be in place. To calculate the need for air conditioning in the room below is no simple way to calculate it: 
The formula: 
Needs AC = (Volume rooms) / 3 * coefficient 
wherein: each volume coefficient 1m3 = 500 BTU / hr. 
For example, a room with a size of 3m x 4m. 3m high 
The need for air conditioning is 
= (P x l x t) / 3 x 500 
= (3m x 4m x 3m) / 3 * 500 BTU / hr 
= 12 m3 x 500 BTU / hr 
= 6000 BTU / hr 
This means that the need for air conditioning room 3m x 3m 4m xt = 6000 BTU / hr. 
1 HP compressor AC = 8000-10000 Btu / hr. ≈ equivalent of 9,000 Btu / hr. 
If the count = 6000 Btu / hr is equivalent to 0.6667 OD. 
It is recommended to use 0.75 OD = 3/4 PK = 7000 BTU / hr, because if there is a decrease 
Air conditioning capacity is still able to cool the room.

For more advanced, can use this formula: 
(L (length) x H (height) x I x W (width) x E) / 60 = BTU requirement 
1 feet = 0.3048 meters 
1 meter = 3.28 feet 
L = Length of room (in feet) 
H = Height Space (in feet) 
I = Value 10 if space is insulated (located on the bottom floor, or coincide with other space). 
Value of 18 if space is not insulated (upstairs). 
W = Width Space (in feet) 
E = value 16 if the longest wall facing north; 
value of 17 if facing east; 
Value of 18 if facing south; and 
value of 20 if facing west. 
Capacity AC based PK: 
AC ½ PK = ± 5.000 BTU / h 
AC ¾ PK = ± 7.000 BTU / h 
AC 1 PK = ± 9,000 BTU / h 
1 ½ PK AC = ± 12,000 BTU / h 
AC 2 PK = ± 18,000 BTU / h 
Example Count: 
Space measuring 3m x 4m or (9 feet x 13 feet), height of the room 3m (10 feet) is not insulated, the long wall facing east. 
Needs BTU = (9 x 13 x 18 x 10 x 17) / 60 = 5,967 BTU air conditioner is equivalent to 3/4 PK. 
So little information on how to calculate AC requirements in accordance with the available room area.