What grade is level f in Reading Plus?

There's no single answer to what grade level "F" corresponds to in Reading Plus. Reading Plus uses a proprietary scoring system, and the grade level equivalent can vary based on a number of factors, including the student's age and the specific content within the "F" level passages. It's not a direct 1:1 mapping to a standard grade level. You would need to consult the Reading Plus program materials or your teacher/instructor to get a precise grade level equivalent for that specific level.