Power Levels

10 : Normal adults/ Chore Boy

11-20 : Seamen Recruit

21-30 : Seamen Apprentice

31-40 : Seamen First Class

41-50 : Petty Officer

51-70 : Chief Petty Officer

71-99 : Master Chief Petty Officer

100-300 : Ensign

301-1000 : Lieutenant Junior Grade

1001-2000 : Lieutenant

2001-3000 : Lieutenant Commander

3001-4000 : Commander

4001-5000 : Captain

5001-6000 : Commodore

6001-7500 : Rear Admiral

7501-9000 : Vice Admiral

>10000 : Admiral/Fleet Admiral

Due to the fact that the pirates ranking from Yonko to noob pirates are kinda ambiguous, I'm using the ranks in the marines as provided by the wiki as a reference to construct the tier for this power levels because it is much more organised and to make it somewhat logical.

Of course there are some exceptions such as Vice Admiral Garp and maybe other characters that I didn't know that their power are way more than their supposed rank but those are the minorities so….. whatever.

As an example, when Luffy set sail in my humble opinion he might be around Lieutenant Commander to Commander level when he defeated Arlong Pirates and that is why he didn't actually managed defeat Smoker on Loguetown and adding to the fact that he still doesn't have a clue regarding Haki and doesn't really have any proper training. While Luffy on Water 7/Enies Lobby arc when using Gear 2nd and Gear 3rd while fighting Lucci might be on the level of Captain because even if he defeated him, it was still a close call that were accompanied with plot armor. And if we take into consideration of the Doukiri power level that has been abandoned by GODA, Lucci measurements was around 4000 not including his devil fruit abilities so it's a fair estimation I guess.