* Credit Hour Definition: A credit hour typically represents 1-1.5 hours of classroom instruction *per week* over the length of a semester or quarter. This is then supplemented with out-of-class work (homework, reading, studying, etc.), which is usually expected to roughly double the in-class hours.
* Course Structure: Some courses might be very intensive, meeting for several hours a week, while others might meet only once a week for a shorter period.
* Diploma Requirements: A diploma requires a certain *total* number of credit hours, not a specific number of hours per credit. To know the total number of hours, you need to know the total number of credits required for the diploma and then look at the typical hours per credit at that institution.
In short: You need to consult the specific college or institution's catalog or course descriptions to determine how many hours per credit are required for their courses. Then you can multiply that by the two credits to find the total class hours for *that specific* two-credit course.