Hawaiian kai, "sea"; also Frisian, Japanese and Welsh origins — sea; ocean; willow. One of the few short names that is native to several unrelated languages.
Kai ranks 93rd among American boys in 2025, with 4,002 born that year. Its best year was 2022, when 5,732 babies were given the name, ranking 59th. The typical living American called Kai is about 9 years old today. It is relatively most common in Hawaii, where it accounts for 0.59% of births.
Source: US Social Security Administration, national and state name files, 2025 release, and the Office for National Statistics for England and Wales. Etymology researched and written by our editors. Living-population and median-age figures are our own estimates, described in the methodology.