How to find your varna from your caste?
Currently, there are two methods, the neo-Vedantin/neo-Hindu way, and the orthodox Hindu way, propounded by orthodox Vedic followers.
- Neo-Hindu way
The neo-Hindu way is based on autonomous self-identification; i.e. you pick your varna.
- The orthodox way
The orthodox Hindu way is based on ancestry, as I show in this answer.
The neo-Vedanta way is more or less a modern invention to suit Western beliefs of "all men are created equal" that British-educated, modern Indians have adopted, whereas the orthodox way is the correct way as per scriptures and all orthodox followers of Hinduism.