Threat range

Each weapon has a threat range for critical hits. Any hit while rolling the d20 within the threat range results in a critical threat (see the critical hit page for more details).

All weapons create a critical threat on a roll of 20, but some have a larger threat range, extending down to 19-20 or even 18-20. Additionally, the Keen and Impact enhancements on a magic weapon will double its threat range, and the Improved critical feat can do the same for all weapons in the matching category (however, those two effects do not stack). A Keen Kukri, for example, has a threat range of 15-20.

Common weapons' threat range
18-20/x2:
 * Falchion
 * Kukri
 * Rapier
 * Scimitar
 * Great Crossbow

19-20/x3:
 * Khopesh

19-20/x2:
 * Heavy Crossbow
 * Light Crossbow
 * Repeating Heavy Crossbow
 * Repeating Light Crossbow
 * Greatsword
 * Bastard Sword
 * Longsword
 * Shortsword
 * Dagger
 * Throwing Dagger
 * Dart
 * Shuriken

20/x4:
 * Heavy Pick
 * Light Pick

20/x3:
 * Battleaxe
 * Dwarven axe
 * Greataxe
 * Handaxe
 * Throwing Axe
 * Longbow
 * Shortbow
 * Warhammer
 * Maul

20/x2:
 * Dart
 * Club
 * Greatclub
 * Heavy Mace
 * Kama
 * Light Hammer
 * Light Mace
 * Morningstar
 * Quarterstaff
 * Sickle
 * Unarmed