Each tooth is worth 10 degrees
Depending on where your sensor is fixed, will determine which tooth to remove.
As Rob says, if you set the engine to 90 degrees BTDC, then mark the tooth that the sensor points to. That will be the least confusing method, and hard to get it wrong. Or, set the engine to TDC and then count 9 teeth from the tooth the sensor points at, in the direction of rotation