Surname Бирсак (Бирсак 
, Birsak 
) , all around the world, is a rare cognomen. The family name Бирсак is characteristic of Austria, where it is quite a rare surname, Netherlands, where it is a rare surname, and Singapore, where it is a very rare surname. Measured by absolute frequency, it is the most numerous in Austria, Netherlands, and Indonesia.
| VARIANT | COUNTRY |
|---|---|
| Бирсак | Russia, Ukraine |
| Birsak | Indonesia, Austria, Singapore, United States, Netherlands |