Family name Kumthornkiat (Kumthornkiat 
) , worldwide, is a very rare surname. The cognomen Kumthornkiat is habitual in South-eastern Asia, particularly Thailand, where it is a very rare surname.
| VARIANT | COUNTRY |
|---|---|
| Kumthornkiat | Thailand |
Samawadee, Wuttipong, and Wattanawadee