At what military rank is his/her letter of recommendation considered to have enough credibility?

Former E-5 here going for civ jobs that may require rec letters. I assume LORs from an O-4 or higher is convincing enough on the officer side, and E-7 or higher for the enlisted side?|||Your assumptions are OK, but there is nothing wrong with a letter of recommendation from someone with rank equal to yours or just above yours. The important thing is what the letter says. A sincere letter from a buddy who values your cooperation, loyalty, honesty, and integrity and can express these qualities well, or give specific examples of these characteristics, can go a long way, compared to a formal letter from an officer who hardly knows you and bases the letter on material gleaned from your personnel file.