Hedera does not officially define “circulating supply,” but maintains a detailed report of “released supply,” found here.
Released supply consists of the portion of pre-minted hbars that have been distributed. Unreleased supply is distributed upon the earlier of its transfer to a network account controlled by a member of the public (regardless of whether such hbars remain encumbered by Hedera or otherwise) or to an operational supply account controlled by Hedera Staff. Public means any individual or entity other than Hedera.
Released supply can be considered one possible method of determining circulating supply; however, different market research and data reporting companies may apply different definitions to certain hbars. The report’s illiquid supply information may inform other methods of determining circulating supply, depending on the nature of the known restrictions. If available, the primary source for the restriction and the location of the restricted coins will be cited in the report, but Hedera cannot guarantee the accuracy of any third-party information.
Some third-party analysis and reporting of Hedera’s circulating supply can be found at the following websites, but Hedera does not endorse any particular report unless specified elsewhere: