I'm not sure. but just want to say that weapons change sizes based on your character sizes. so the way to get the biggest is to put them on jora or use a guild lord tonic.
sword> obsidian edge!!!!! how did this get over looked :/ i'm dissapointed in all of you LOL jk guys you know i love you.
axe > pryoclastic
shield> for me i think mursaat> or possibly draconic. they seem big for me.
It may be ulgy, but Brute Sword is the second largest sword in the game next to Fellblade. I don't say they are the longest, just the most massive swords known
Swords like the long sword, and runic blade are long but not very big since they're thin. If you look at width as well as length it's probably the fellblade that's the biggest. Charr sword is pretty big also.
Swords: the Long Sword is the LONGEST, yet the Fellblade is indeed bigger. Both the Deldrimor Sword and the Colossal Scimitar are close to it sizewise.
Axe: Deldrimor Axe. No doubt. Way bigger than anything mentioned here.
Shield: Deldrimor shield, again. Tormented is pretty flat but rather big nonetheless.
Shield of the dead is enormous, Aurate Aegis is pretty big too. I like the tyrian hand axe for size, tribal axe is huge too. Fellblade is probably the biggest sword.