Rules Index | GM Screen | Player's Guide

Chapter 8: Playing the Game / Movement / Cover

Cover and Large Creatures

Source Player Core pg. 424
If a creature between you and a target is two or more sizes larger than both you and your target, that creature’s space blocks the effect enough to provide standard cover instead of lesser cover. The GM might determine that a creature doesn’t gain cover from terrain that it’s significantly larger than. For example, a Huge dragon probably wouldn’t receive any benefit from being behind a 1-foot-wide pillar.