Source: Board of Governors of the Federal Reserve System (US)
Release: H.4.1 Factors Affecting Reserve Balances
Currency in circulation includes paper currency and coin held both by the public and in the vaults of depository institutions. The total includes Treasury estimates of coins outstanding and Treasury paper currency outstanding. This definition of currency in circulation differs from the currency component of the money stock, a measure of currency used in some other Federal Reserve reports (for example, the H.6 release), which excludes currency held in vaults of depository institutions.
Board of Governors of the Federal Reserve System (US), Liabilities and Capital: Other Factors Draining Reserve Balances: Currency in Circulation: Wednesday Level [WCICL], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/WCICL, March 22, 2023.