I read somewhere that about 1% of the world population hold at least $100 in BTC.
That is completely false. There are only 6.3 million addresses holding more than 100 USD, and even if that was one per person (which clearly is not the case, as most wallets are the sum of several hundred addresses), that would be less than 0.1%. My personal estimate is less than 0.01%.Yeah! That's true, suppose if 1% of the world population holding at least $100, it sums up total holding worth to be at least $700B which is too high from real. But also 0.01% isn't convincing estimate since 0.01% only adds-up to 7M people and only Coinbase reports 10M+ customers so I think right count is somewhere between 0.1-0.4%.
Now about price, With every 1% increase in adoption, we can assume 20x for first increase, 2x after second increase, 120% after third and so on..
So suppose today price is $11K, if 1% of additional world's population start using Bitcoins, price will go to $220K, $440K when additional 1% of the population start using it, $528K with another 1% and so on.., this is my personal estimates based on so far run of Bitcoin.
how did you arrive at this calculation? Namely if additional 1% starts using bitcoin, the price goes up 20times?
simply put the price would increase, the increased use means an increased demand and given supply is fairly fixed (it's still growing slightly until the cap of 21m) then price would increase. 
