The fuel tank capacity of Maruti Suzuki Ciaz is 43 liters. For the cars with manual transmission the fuel efficiency is 20.65 km/ liter and for those with automatic transmission, it is 20.04 km/ liter. Any car that has a fuel effeciency higher than 16.5km/liter is pretty good according to me.
Now, it also depends on your driving style to determine how long the fuel would last. In certain terrains the engine has to work more to pull the car and thus burns more fuel. It burns more fuel if you drive at a higher RPM. You would probably get a higher mileage on the highways as compared to cities and hilly areas. Also, if your car is well maintained then the fuel consumption would be lower and the efficiency would be higher.