The rating is determined by the energy efficiency ratio
Every AC has an Energy Efficiency Ratio (EER) written on it. If EER is written from 2.7 to 2.9 on an AC, then it is one star rating, 2.9 to 3.09 two stars, 3.1 to 3.29 three stars, 3.3 to 3.49 four stars and above 3.5 it is 5 star rating. There will be AC. The cooling output and input power of the AC should be calculated for the energy efficiency ratio. This can be checked while buying the AC, which is written on the plate. For this, if you divide the power input into the cooling output, then the rating will come out.
Learn AC ratings like this
All ACs are of one ton and their cooling output is 3516 watts. This output will give the division of the input. For example, if an AC is taking 1250 watts of input power, then if you divide 1250 in 3516, the result is 2.00. If you see it in the EER table, then 2.00 will be found in the rating of one star. Hence this AC is of one star rating. Similarly, if the input power of AC is 11750 watts, then dividing by 3516 will give 2.99. Looking at the table, 2.9 to 3.09 rating is in two star rating and it will be of AC to star rating. In this way all star rating can be calculated.