It depends on the type of engine you have in your Belta and how well-tuned the vehicle is, and finally, your driving style. For example, I have a 1.3 lit 2007 model Belta X. With a nice, clean air-filter, semi-synthetic engine oil and properly inflated tires, it easily gives me 13 km/lit in city driving, with AC. On highways, it has given me anywhere from 16 to 18 km/lit, again with AC.
If you drive your Belta somewhat gently, i.e. don't engage is brisk acceleration every now and then and keep the engine happy, you should be able to attain the above-mentioned figures with a 1.3 lit Belta. Happy motoring.