The standard answer I've received on this question from professors and 2 and 3 L's is to expect to study about 2 hours per hour of class time. It was not uncommon or unusual to study 8 hours a week, for example, for Torts alone.
All told, including class, my average week was between 46-50 hours per week of total work. Memo's add to the fun and when you have a test coming off, all bets are off.
There were some weeks when I put in closer to 60 hours and rare weeks when I had less than 40 hours (including class time).
During finals, I studied 40-50 hours for Contracts, 55 hours for torts, and 50 hours for Property.
During the semester, I wrote 3 memo's, the first being 10 pages long, the second being 14, and the third being 12. The memos soak up a lot of time as you have to research, plan, write, edit, double check, and finalize.
The roughest weeks were when memo's were due and the two times our professors scheduled make up classes, which happened to coincide with the heaviest reading (by chance - no one is that cruel).
I also carefully tracked my reading. The average reading weeks was between 90 and 120 pages, with the heaviest week requiring close to 200 pages.
Law school requires a major investment of time and effort. Expect to work harder than you ever have. If you've come from the "real" world and worked a job with real responsibility, the workload is manageable. If you are used to college course work and "cramming", you may struggle to adapt to the workload. I still don't think you can cram for law school with the success it can be done in college (just my opinion).