four percent - 4% - ?

[CyndiA1]

I want to say that the promo material at the start of the book is four percent of the total content.

I've looked it up, and it seems that for formal writing that is not scientific that I should write out percent. Examples are: 10 percent, 27 percent.

I know numbers below ten are written out. But, the examples show a numeral but not a smaller one.

Is "four percent" correct.

I think the point I'm making is important, but with style manuals differing and no specific guidelines, I may just remove the paragraph. An editor can dock 10 points under grammar and then more under subjective for errors. That can certainly impact on creativity and content.

[EvaDar]

I can't predict what an editor will do, but this site refers to several different style guides.
https://www.proofreadnow.com/blog/3-rul ... ercentages

Whether to spell out percent or use the % symbol is largely a matter of style, as is using numerals versus spelling out the numerical values. The Chicago Manual of Style, for instance, says that percent is usually used in nontechnical contexts, while % is more common in scientific and statistical copy. Numerals are used in all instances with percent except at the beginning of a sentence.

The AP Stylebook always spells out percent because the symbol doesn’t translate between AP and newspaper computers. It also always uses numerals with percent except at the beginning of a sentence.

Both the AMA and APA style guides say to use % with numerals in all cases except at the beginning of a sentence.

Some clients have their own style. The important point is to apply whatever style you choose consistently.

So, bottom line is be consistent. Pick a style guide and use those rules for both the number and the symbol. That way, you will have a source to back you up if you need to get a recheck.