According to Kemper's formula: A person need a total of 0.06624605 BTC in order to guarantee wealth worth $1 million.
I ask myself once this happens, how worthful 1$ million dollars is going to be... With accelerated inflation, our fiat currencies, including dollar, are leading us to loss of purchasing power along the years. Central banks keep printing money, raising wages, while products and services also increase in costs. In the end it's just a makeup to give the masses the impression the economy is thriving.
The only thing thriving for real is the number of digits on our daily transactions. What you could acquire before for 10$, now you need 100$. What costed 1000$, now costs 10,000$... At some point to be a millionaire won't mean a big deal anymore.
So, be prepared to hold much more than 0.06624605
BTC if you aim life quality and stability.