Pathfinder Flanking Rules
Flanking is one of the most tactically satisfying mechanics in Pathfinder — the moment when positioning clicks into place and a rogue's sneak attack damage suddenly doubles the pressure on a cornered enemy. This page covers the precise definition of flanking under Pathfinder rules, the mechanical steps required to trigger it, the situations where it applies cleanly versus where it breaks down, and the judgment calls that come up at most tables.
Definition and scope
In Pathfinder (both the original and the second edition published by Paizo), flanking is a condition that grants a melee attacker a specific bonus when at least 2 allied combatants threaten an enemy from opposite sides. In Pathfinder First Edition, flanking grants a +2 circumstance bonus to attack rolls. In Pathfinder Second Edition, the attacker gains the flat-footed condition on the target (equivalent to a -2 to the target's AC), which indirectly benefits every attacker against that creature, not just the flanking pair (Paizo Core Rulebook, PF2e, p. 476).
The scope of flanking is strictly melee: a character must threaten the target with a melee attack to participate in a flanking pair. A ranged attacker standing 30 feet away does not contribute to flanking, regardless of how helpfully positioned they look on the map.
Flanking is also the primary unlock for a rogue's Sneak Attack ability, which makes it one of the highest-leverage positioning decisions in the game. Getting flanking right — or getting it wrong — can swing a combat round by 2d6 damage or more, which is reason enough to understand the geometry.
How it works
The flanking check is fundamentally spatial. For two allies to flank a target, they must both occupy squares (or spaces, in gridless play) on opposite sides of the target. "Opposite" is defined by Paizo using a line test:
- If that line exits through a square on the far side of the target that is occupied by the second flanker (or passes through it), flanking is established.
- The flanking bonus applies to all melee attacks made by either flanker against that specific target for as long as both remain in position.
A creature with a larger space complicates the geometry usefully. A Large creature occupies a 2×2 square footprint, which means a 3rd-level fighter and a rogue can flank it from adjacent squares on the same side of a corridor — provided the line test still passes through the creature's footprint to the other flanker's square (Pathfinder First Edition Core Rulebook, p. 197).
Common scenarios
Standard corridor fight: Two medium creatures, one on each side of a humanoid enemy. Clean flanking, no ambiguity. The +2 bonus (PF1e) or flat-footed condition (PF2e) applies immediately.
Diagonal positioning: This trips up new players more than anything else. Two flankers positioned at 45-degree angles from each other relative to the target may or may not pass the line test depending on the exact squares involved. Running the line is the only reliable method — eyeballing diagonals produces table arguments.
Large and Huge creatures: A Huge creature occupying a 3×3 space can be flanked by allies positioned on opposite sides of its full footprint. This actually makes it easier to establish flanking geometry, since more squares qualify as "opposite."
Reach weapons: A character using a reach weapon (typically threatening at 10 feet rather than 5) can participate in flanking from further away — the flanking line still applies, just from a square further back.
Mounted flankers: A mounted character threatens from the mount's space, not the rider's anatomical position. This matters when calculating the line.
Decision boundaries
The cleanest decision boundary in Pathfinder flanking is the line test vs. the eyeball test. Most table disputes come from players declaring flanking based on visual impression rather than running the actual geometric check. The Pathfinder rules are unambiguous that the line must pass from one flanker's center through the target's center and out the far side into the second flanker's space.
The harder boundary is threatening vs. not threatening. In PF1e, a character must be capable of making attacks of opportunity to count as threatening. A flat-footed character, a character who has already used their actions, or a character wielding a ranged weapon does not threaten — and therefore cannot complete a flanking pair no matter how well-placed they are on the map.
PF2e simplified this: flanking requires only that both allies are adjacent to the enemy (within reach) and able to act. The removal of attacks of opportunity as a baseline mechanic in PF2e means the threatening check is less fraught, but the position requirement remains identical.
The other boundary worth flagging: mindless creatures and flanking immunity. Creatures with the mindless trait in PF2e are immune to the flat-footed condition from flanking specifically, which means the entire tactical premise evaporates against animated constructs and certain undead. Checking the creature's stat block before committing to a flanking formation is a habit worth building.
For a broader look at how tactical mechanics fit into Pathfinder's design, the /index covers the full scope of rules topics on this site. The mechanical framework behind action economy and conditions that interact with flanking is addressed in /how-recreation-works-conceptual-overview.