What I have learned from reading this forum and other retirement/finance/blogs/you name it, is that you start with what you will need and fit your portfolio to deliver the funds that you will utilize.
Find your number by building from the ground up. You will need a few years worth of budgeting numbers to figure this out. The more years the better. Then add wants and a fudge factor. Plug that number into multiple retirement calculators based on whatever SWR you want (4%) get you total portfolio number and there you go.
example:
Basic living expenses: 25k
Everything else: 10k
Fudge factor/cushion 5k
Total: $40k
The key to remember is you can adjust it however you want in retirement. When you run it through firecalc or any calculator it is basing the withdrawals on consistency no matter what the market is doing. 4% SWR plus 3% inflation on the $1million portfolio will look similar to this:
Year 1 $40k
Year 2 $41200
Year 3 $42436
Year 4 $43709
Year 5 $45020.....etc.
So if you plug $1million in to firecalc at 3% inflation and 4% SWR and you get a comfortable success rate, then you are there because what I have noticed is that even though firecalc says you will succeed with the above numbers, the human element comes into play during actual use.
I don't have any exact figures but when all hell was breaking loose in 2008/9 the majority of the online chatter seemed to be: "I am going to withdrawal less this year because of the market and because I can cut back on bacon and beaver cheese" doing this you go from a 95% success rate from your plans to >95% success rate because of how you adjust based on the current data and your fears/experience/expectations.
If year 4 was 2008 then I only took $40k out again because I am cutting back and the market was bad. In year 5 (2009) I did the same b/c I could still live comfortably and who knows if the market will ever recover?
I'm not saying that is bad, but I almost feel some people will get caught up in the 'one more year' syndrome when they could have retired earlier based on getting to a 110% success rate or such a low SWR.
In the end it is what
YOU are comfortable with because no matter what gets written by which 'professionals' if it all goes to crap the're not going to bail you out.