Sometimes we can use whether and if interchangeably, but we also need to know which condition where only one of them is correct to use.

1. Whether and if are interchangeable in response to/in relation with a yes/no question

Do you think they will win? 🡪 I wonder whether they will win. 🡪 I wonder if they will win.

Do we need to take the bus? 🡪 I am not sure whether we should take the bus. 🡪 I am not sure if we should take the bus.

1. Only use if to introduce a condition

If today is sunny, I will take my dog to the park. – correct 

Whether today is sunny, I will take my dog to the park. – incorrect 

1. Whether clause as subject

Whether he is rich is not important.

Whether I like it or not is none of your business.

1. Before an infinitive, use whether

I’ve been wondering whether to leave or to stay.

1. Use whether to say either way; use if to highlight the condition that should be met

Let me know whether you like it. 🡪 no matter you like it or not, you should let me know

Let me know if you like it. 🡪 in case you like it, you tell me; if not, do not let me know