In most cases it is a minimum of 3 times the month rent gross as an income from employment. An example:
Rental price apartment = 2.250
Then your income needs to be 2.250 * 3 = EUR 6.750 gross as a minimum.
In some situations also 4 times the month rent is required. So it can differ per property and is always good to ask or discuss with your rental agent. In a lot of cases when you are with a partner, this income can also be accounted for (not always in full).