In the sheet below, I compare six countries in terms of nominal per capita GDP (in US dollars equivalent). These have to be reinterpreted in terms of purchasing power parity, i.e. if local prices are lower, you can enjoy the same things for less money. (Nominal and PPP terms are taken from slightly different IMF surveys, but you get the idea.)
The last couple of columns answer the question, "How much income would each national need, to match America's standard of living?"
Doubtless there's problems with the methodology - PPP may well change as each country's nominal GDP increases. And it seems clear that the whole world can't live exactly like Americans do today. (It's also interesting to note that pricey, high-tax countries like the UK and Japan can't catch up with the USA without exceeding the latter's per capita GDP.)
But on these figures, China could match American living standards, on a quarter the income. So the low-pay trading advantage it enjoys is huge now, and is likely to remain so.
And look at India and Vietnam - they'd only need about one-fifth American per capita income to have the same in PPP terms. In fact, they could out-compete China in labour costs, which is one reason for China to move away from labour-intensive work like trainer-stitching, and towards heavy industry.
So Vietnam undercuts China undercuts America...
And given India's enormous population, its higher proportion of cultivatable land (compared with China), its well-established political and legal institutions, and its many millions of English-language speakers, it may be that India is the economy to watch this century.
IMF per capita GDP figures quoted from Wikipedia here (nominal) and here (PPP).