Acorn Woodpeckers (Melanerpes formicivorus) are known for storing acorns in granaries, yet the relationship between acorn size and hole dimensions is not well understood. We measured acorn–hole pairs in Butte County, California, during fall 2024 to assess how acorns fit within their storage holes. Among 126 pairs, acorn width strongly predicted hole width, though this link weakened for the largest acorns. Acorn length also correlated with hole depth, but less consistently, as holes were often deeper than the acorns they contained. Video footage showed behaviors such as testing fit-checking, removing, and repositioning acorns. Despite variations in insertion angle and depth, Acorn Woodpeckers appeared to choose holes appropriately sized for their acorns, suggesting deliberate placement rather than random use. Although multiple oak species fruited concurrently, all stored acorns were from valley oaks (Quercus lobata), suggesting that hole size may be optimized for this species. Most granaries occurred in grey pines (Pinus sabiniana), which have been heavily impacted by wildfires. The loss of these trees could reduce suitable storage sites and pose challenges for Acorn Woodpecker persistence in affected areas.