Family name ฤทธา (Power 
, ฤทธา 
, Rittha 
) , in the world, is a common last name. The cognomen ฤทธา is characteristic of Ireland, where it is a common surname, Guernsey, where it is quite a common surname, and Australia (explore the name in all countries). Measured by absolute frequency, it is the most numerous in the United States, the United Kingdom, and Canada. Much less frequently, ฤทธา is the forename as well as the last name.
| VARIANT | COUNTRY |
|---|---|
| Power | United Kingdom, Ireland, Canada, Australia, United States |
| ฤทธา | Thailand |
| Rittha | South Africa, India, Brazil, Malaysia, Thailand |
Reinghttha, Ritta, and Ruetha