It depends on the position you are being interviewed for.
1. If you are a skilled worker (carpenter, welder, cook, etc.) the interview takes about 15-20 minutes and it's mandatorily followed or preceeded by a test where you get to prove your skills. The test is much more important and decisive than the interview.
2. If you are being interviewed for an entry level position that doesn't require special technical or language skills (for example waitress) the interview takes about 20 minutes. If the job you apply for requires additional skills (like French, German, or IT skills like SQL, Linux, C++ just to name a few) the interview will be 20-30 minutes, language skills may be tested during the interview and you may be asked to come later or to stay after the interview for additional IT tests.
3. If you are being interviewed for a middle level position (for example experienced salesman), expect the interview to last 30-45 minutes.
4. Finally, for a manager position, interviews can take up to 2 hours and there may be several than one.
Also, when you are scheduled for the interview, it's more than ok to ask for the time you should reserve, especially if you take time from work or from school to go there. The recruiter should normally tell you about the length of the interview and tests but if they don't, just ask.