I'm shortly to begin my four months of penitence at the University of Rostock, so how fortuitous it was for me to come across an article reporting on, inter alia, the average study times of European students. It seems that Portuguese university students spend 41 hours a week, on average, either in class or studying, while British students merely manage a measly 26 hours a week. Germany comes in at about 33 hours per week. The results have, as always, some problems. First, the numbers are self-reported by the students, who, as the article notes, "may have considered time spent in the college bar as indistinguishable from any other period of study." Second, though I'm sure I could find it if I cared enough, there's no indication as to the distribution of the data--I'd be interested to see at least what the median study time was. And third, the composition of study time is sorely missed; it would be more illuminating to see the breakdown among countries between time spent inside and out of class.
How American students square up is, of course, an interesting question. At my university, several of my professors espoused what I call the "time-and-a-half-rule." Namely, students were (or at least could be) expected to spend 150 percent of the time spent in class preparing for it outside class: in other words, a student in a normal three-credit class was expected to spend 4.5 hours per week studying for the class in addition to the time sitting in lecture. Assuming a typical 15-credit semester, this meant that a student could be expected to spend around 37 hours a week either in class or studying. If my university is typical, that would put the US near the top of the chart--and really, there's no reason to think it would be any less accurate than the other numbers.
In any event, I'm quite certain that I'll be dragging down the German average for the few months I'm here.