I agree with themadpatter. Too many peoples hackles get raised with the word "rule" but as mad pointed out the Fibonacci sequence, also known as the golden ratio (and also the golden rule, which I think the OP was striving to get the answer for) is most pleasing to the eye and appears in nature over and over again from seashells to sunflowers (hence why most find it appealing to the eye yet don't even know why, it is almost as though we are hard wired for it) Here is an excellent article written by Jinny Beyer regarding it and calculating border widths.
https://jinnybeyer.com/golden-ratio-...s-for-borders/