Let's do the maths.
1. Remember - 0.75/0.8 Ton AC delivers 9000-9500 BTUs, 1 Ton AC delivers 12000 BTUs, 1.25 Ton AC delivers 15000 BTUs and 1.5 Ton AC Delivers 18000 BTUs.
2. Calculate your Room Size in Sq fts. For e.g., a standard room size is 15 X 12 ft. That means 180 sq ft.
3. Multiply Room sq ft X 25 BTUs. For e.g, 180 (sq ft) X 25 = 4500 BTUs.
4. If Room is in shade then decrease the BTUs by 10%. Similary if Room is directly under Sun then increase the BTUs by 10%.
5. Each Person add around 600-700 BTUs. Suppose three persons are present in the Room, then add another 2000 BTUs.
6 Kitchen are generally Hotter and hence, add another 2000-3000 BTUs.
What I Practically found (Personal Room with door not opened often and Room is properly Air Tight with not a small opening) -
1. If a Room sq ft is below 100 sq ft, then go for 0.75/0.8 or 1 Ton AC. That will be enough.
2. If a Room sq ft is between 100-200 sq ft, then go for 1 Ton AC. That should do.
3. If a Room sq ft is above 201-300 sq ft, then go for 1.25 or 1.5 Ton AC.
4. If a Room is big say above 301-500 sq ft, then better go for 1.5 Ton AC.
5. If Space is bigger than 501 sq ft, then it may required more than 1 AC.
Another Few Important Factors to look for -
A 1 Ton AC may cool your Room and you may not need a 1.5 Ton AC. But what about the power consumption? What about your electricity bills. Three important factors must be known before buying the AC. After choosing your Desired Capacity of AC from above stats check for 3 important factors - EER (Energy Efficient Ratio), COP (Coefficient of Performance) and Star Ratings.
*Higher the EER, lower the electricity bills.
*Higher the COP, lower the electricity bills.
*5 Star Ratings will give lower electricity bills then 2 or 3 Star Ratings.
Split AC or Window AC - There is no preferred choice, but Split AC is modern and looks beautiful than Window AC. It depends on EER, COP and Star Ratings as mentioned earlier, whichever has better go for that. Personally if you ask me, then Split looks beautiful to your Room and takes less space.