What is the difference between a King and a California King?

The following provides details on differences in dimensions of a king vs. California king:

A standard King size W: 76” x L: 80” mattress is slightly shorter (-4”) than the California King, but also slightly wider (+4”).

The California King size W: 72” x L: 84” mattress is thus slightly longer (+4”), but also slightly more narrow across (-4”).