Weapon Rank

From Fire Emblem Wiki

Weapon Rank is a weapon's ranking on a scale of E - D - C - B - A - S - Prf, from weakest to strongest. It should be noted that Prf does not always have the most powerful weapons; many are, but they are unique to certain characters. Otherwise, the general rule is that S has the most powerful, while E has the least. Sometimes, using weaker weapons is a good idea, such as against enemies much weaker than you or in a link arena, where there are bonuses for using weak weapons and penalties for using strong ones.

In some cases, a unit can't advance to S weapon rank if they have not yet promoted. For example, in FE8, Joshua can't travel past A-rank as a Myrmidon. The Rank of a weapon specifies how hard the weapon is to wield. In general, weapons of higher might have a higher Rank, but this not always the case, such as with the Devil Axe. The Weapon Rank system is used as a replacement for the weapon level system.

N.B.: Weapons in Fire Emblem Radiant Dawn may have SS ranking, only available at top-tier promotion.