According to the Deutsches Studentenwerk, an average student will need approx. 700 EUR per month, including accommodation, food, transport, leisure and other personal costs.
If you are an international student applying for a study visa in Germany, you will be asked by the German Embassy to provide evidence that you will have beween 565 and 650 EUR per month available for your living expenses in Germany.
Make sure that you have enough money available for the first few days after arrival, as there will be lots of initial expenses such as your room deposit, registration fee, season ticket for public transport, etc. Please note that if you use bank cheques you will not have access to the money until the cheques have been cleared and the money credited to your account. This can take up to two weeks.
Of course, the cost of living will depend on your personal lifestyle, but keep in mind that living abroad always stretches one's budget. However, the overall cost of living in Germany is fairly affordable for students.
Further information: