I think it will depend upon the university. In teaching universities it is generally about 9 credit hours per semester which translates approximately about 9 hours of lectures plus another 6 hours of lab work. In a research university that gets reduced by 6 credit hours per week. This works well and provides sufficient time for research activities.
In my country this is regulated by three different laws, such as Act of Higher Educatin, Act of Public Servants' Law and Act of Labour.
Working hours for every public servant (school teachers, professors, employees of the helth or culture etc.) is 40 hours weekly. In the higher education, the number of teaching hours is minimum 10 per week .
Each of Hungarian colleges and universities has its own regulation declared by the governing body (senate) that how many teaching hours different positions (professors, and lecturers) should have.
At my university, a full professor has 10 teaching hour per week while an assistant professor has 14. Number of teaching hours are counted by the "electric study system" and controlled in average of two (autumn & spring) semesters.
Just to answer your question, I teach 185 hours per semester but regarding to our special situation that, having too many part-time students, the number of my teaching hours is 4 in weekdays and 8-10 in weekend. I think, it is not too much but would prefer to teach more in weekdays and less in weekends.