The sha1 hash for 64test64xa is 6779c53432b8badf049bb9d8924a5785dd887243 which is 41 characters only using hexadecimal, 10digits and 6letters. But how long it would be if it was using the whole 26 letters in the latin alphabet? What if it also differentiated between UPPER and lower cases?
If you’re using Linux (or macOS or MinGW or CygWin or MSYS), you can do something like this in the terminal:
xxd -r -ps | base64
The first command will read the standard input and decode hex strings back into raw data, and the second one will do base64 to the output.
If I pass the hex string mentioned in your original post through this command, I get: