A semester hour generally represents one hour of classroom instruction per week for one semester. However:
* Some courses have more than one hour of classroom instruction per week. A 3-semester-hour course might meet three times a week for one hour each, or it might meet twice a week for an hour and a half each. The total weekly contact time varies.
* Many courses include significant out-of-class work. A 3-semester-hour course might only have 3 hours of classroom time but require 6-9 hours of homework, reading, and studying per week. The semester hour reflects the total workload expectation, not just classroom time.
* Different institutions have different conventions. Some might weigh lab hours differently than lecture hours.
Therefore, you can't reliably convert semester hours directly to classroom hours. The syllabus for a specific course is the only reliable source of information about its class meeting times and total workload.