If I get a job offer, how do I politely ask them how long I have to make a final decision whether I want to join them or not?

I recently have applied for multiple jobs. As a result, I have had a few interviews. All of them went well. Some of the companies I want to work for more than others.

If one of my second-choice companies calls me back to make an offer, how do I ask them “how long do I have to decide whether I want to work for you or not”? I feel like blatantly asking how much time I have to decide if I can work for them or not sounds too rude, like I am saying “I am waiting to hear back from other companies that I would prefer to work for before I make any final decisions with you.” and makes it sound like I was never interested in the job to begin with.

So how do I phrase this in a professional manner if an offer is made, without ruining my relationship with the company before I even start (potentially) working for them?