What is the average adult human skull's circumference?

The average adult human skull's circumference is indeed approximately 22 inches (56 cm). This measurement typically represents the overall size of the skull, which can vary somewhat among individuals due to factors like sex, age, and ethnicity, but this figure provides a reliable general standard in anatomical studies. It is important for various medical and forensic applications to know the typical dimensions of the skull, which can also aid in areas such as cranial surgery and the creation of fitting prosthetics or helmets.

The other figures do not align with the accepted average; while they may represent some individual variation, they fall outside the range considered typical for adult males and females in general anatomical references.