u can determine it urself.
-Dont full ur cng tank, fill it like lets say 300 rupees instead of goin to 450.
-Repeat the same for 2 weeks
-Reset the trip meter each time, while noting the millage
-take out the average, u would know about it, it should give u around 25+ per kg, else change ur driving style and get the car tuned, including the tire pressure