The easiest way to figure it out would be to take the difference between age you think you'd normally retire at and the age you think you'd live to. Take that number of years and divide the million by it.
Take that number & multiply it by the difference between your current age and normal retirement age, then add the original million.
So if you expected to retire at 68 and based upon family history you could expect to live for another 30 years, you'd divide the million by 30 or $33,333 per year.
Let's say you're currently 40, 68-40=28. 28x$33,333 = $933,324. Add the original million and you'd need $1,933,324. And this is without including inflation.