Updated - How long your resume should never be:
Bottom Line: A couple of years ago I shared research that the most popular and desired length of a resume by hiring managers was one page. At that time the most commonly submitted resumes were two to three pages. That's a disconnect that can work to the disadvantage of the candidate. It probably won't surprise you that longer resumes aren't back in vogue. In fact, the updated research demonstrates that there should probably never be a resume that's longer than a page unless it's specifically called for by the employer.
A top expert at 42Hire/Medium said that anything more than a page will virtually ensure that your resume won't be carefully examined (the average length of time a resume is scanned is 15 seconds the first time) and will most often be a liability to your prospects. The piece noted that recent resumes presented by Elon Musk, Hillary Clinton and Marissa Mayer were all one page.
If the founder of Tesla, Solar City, Space Ex & (a new company I haven't investigated yet) can fit all of his particulars on one page. We all can! The point is that your effort is almost always going to be best served by figuring out how to fit your best stuff onto one page, rather than trying to seem impressive by filling out multiple pages.
That reminds me of one of my favorite sayings. Impressive people generally don't have to tell others they're impressive.