link changed, here's a more permanent one: https://www.nber.org/papers/w29396

jack

bitcoin

0.01% of Bitcoin holders control 27% of all circulating coins

Relevant bit from the research: 

> [...] We show that while the balances held at intermediaries have been steadily increasing since 2014, even by the end of 2020 it comprises only 5.5 million bitcoins, about one-third of Bitcoin in circulation. In contrast, individual investors collectively control 8.5 million bitcoins, almost half the bitcoins in circulation by the end of 2020. Within individual holdings, there is significant skewness in ownership.

Full paper here: https://www.nber.org/system/files/working_papers/w29396/w29396.pdf -- ownership concentration is discussed on page 26. Beyond the headline, the paper shows interesting figures such as real volume breakdown by entity type, clustering relationships between exchanges, and how the researchers calculate and visualize clustering.

