Is it correct to say "please let me know if you need help" or must I use "whether"?

The phrase "please let me know if you need help" is grammatically correct and commonly used in both formal and informal contexts. It is a polite way to offer assistance without imposing it on the recipient. The word "whether" is typically used to introduce a choice between two alternatives, so it would not be necessary or appropriate in this context.

For example, if you were offering a choice, you might say, "Please let me know whether you need help with A or B." However, if you are simply offering help without specifying alternatives, "please let me know if you need help" is the correct and more natural choice.

This phrase is widely used in various settings, such as customer service, education, and personal communication, as seen in examples from retail greetings and educational contexts12.