You can use Roscoe formula to determine the sample size, Count all the items of your questionnaire (Except the Demographics) when you have counted them, multiply it by five and the value you will get will be your sample size.

Rosko Fourmula= Sum of your Item (Questioniares ) * 5.

Readings:

https://jasemjournal.com/wp-content/uploads/2020/08/Memon-et-al_JASEM_-Editorial_V4_Iss2_June2020.pdf

http://studentsrepo.um.edu.my/3186/5/CHAP3.pdf

There are many sites that can help you also, Kindly do check them out as well.

Hello Lakmali Rupasinghe

It depends on your research.

As a shortcut, click: https://www.calculator.net/sample-size-calculator.html