1000 Billion $ in circulation (http://www.federalreserve.gov/faqs/currency_12773.htm rounded for easier calculation)
7 Billion people
= $142.85 per person

If 21 million coins are fully out and mined / 7 billion people
= 0.003 Bitcoins per person

So if instead the market cap was 1000 billion $ into bitcoin / 21 million coins
1 btc = $47,619

Or in other words doing it backwards $142.8571429 / 0.003 BTC = $47,619

If everything is priced in bitcoin, then the new "$20 worth of stuff" is then 0.0004 BTC

This is just replacing the national currency, not world currency in circulation, or store of value, or remittances etc. which would bump it up a lot higher as others on the forum have already said and also in videos done by Stefan (https://www.youtube.com/watch?v=Cs6F91dFYCs) and James Angelo (https://www.youtube.com/watch?v=g2nXgK34HIM) have also reported.

Most of you probably already know these calculations so its basically a repost I guess, but i just wanted to help noobs coming in here to know how much they should risk. The question you should ask yourselves is if bitcoin goes mainstream and reaches 1000 Billion market cap, each bitcoin you purchase is a chance for it to reach $47,619. So to people out there still thinking about buying bitcoin, think about it. You can spend $700 or so and lose that all in 1 night binary outcome on blackjack or roulette, or you can do another bet and pick up 1 bitcoin that may not be a binary outcome (others may argue it is) and at least fluctuate in price between $1 - $47,619+ over the next 10 years instead of a single night that you double your 700 to 1400 or it goes to 0. No in between.

So even if you do not know anything about bitcoin, this play should be both fun and interesting to look at to just secure 1 bitcoin and forget about it period.

(btw when I refer to 700, i'm just rounding up the current price of bitcoin the past week at the time of this post)