Gotta have 300,000 saved for every 1,000 you want to take out per month. Ex: If you have 1,200,000 saved you should be able to take out 4,000 a month and not have to worry about running out of money. Of course this is only the case if that 1,200,000 is invested in something that averages a 7-8% gain annually. As far as how much you should have saved up, depends on where you live and what your lifestyle is.
TLDR; Take out 4% of your retirement fund each year and you should be fine