Does a cover letter have to be one page?

Yes, a cover letter does have to be one page.

Recruiting managers only have time to read a one-page cover letter. A two-page cover letter is something they just don’t have the time to read.

The shorter your cover letter is, the easier it is for recruiting managers to read and understand. So when you’re writing your cover letter, try to write a short cover letter that describes your main achievements and explains why you’re the best candidate for the role.