Please explain the reason why you are asking the question if you want a more accurate answer.
Generally, company decides how many days of notice it needs in case of separation (resignation / termination) and puts it in the appointment letter or it may put it in the HR Policy and intimate to the employees. However they must agree to the change, otherwise it has no validity.
If nothing is specified, you need to refer to the Model Standing Orders of the state where you are based and follow that as a benchmark.