The FTSE index that's used by the Vanguard total world fund is free float, and the US is about 45% of the free float total global stock market. You can find that on the relevant Vanguard or FSTE webpage. This data http://data.worldbank.org/indicator/CM.MKT.LCAP.CD/countries/1W?display=map
from the World Bank may help you answer your question. Push the "table" button to see country specific data. I'm not able to embed the map in this post, but it clearly, graphically shows that China has the second largest total public market cap after the US. But I'm pretty sure that nearly all of these large Chinese companies are still mostly state-owned companies: only, say, 10-20% of the shares available in the market. Based on this I'll guess that China accounts for the bulk of the difference between the global free float and total market cap numbers. The rest of the difference would be partially state owned companies in other countries, e.g. France, and companies where founding families still own large stakes, e.g. News Corp.