BIT_COUNT (Transact SQL)
Applies to: 
SQL Server 2022 (16.x)
Azure SQL Database
Azure SQL Managed Instance
SQL analytics endpoint in Microsoft Fabric
Warehouse in Microsoft Fabric
BIT_COUNT takes one parameter and returns the number of bits set to 1 in that parameter as a bigint type.
Transact-SQL syntax conventions
Syntax
BIT_COUNT ( expression_value )
Arguments
expression_value
Any integer or binary expression that isn't a large object (LOB).
Return types
bigint
BIT_COUNT doesn't cast, before counting the number of bits. This is because the same number can have a different number of ones in its binary representation depending on the data type.
For example, SELECT BIT_COUNT (CAST (-1 AS SMALLINT)) and SELECT BIT_COUNT (CAST (-1 AS INT)) return 16 and 32 respectively. This is intended, as the binary representation of -1 can have a different number of bits set to 1 depending on the data type.
Remarks
Distributed Query functionality for the bit manipulation functions within linked server or ad hoc queries (OPENQUERY) aren't supported.
Large object (LOB) data types in the Database Engine can store data that exceeds 8,000 bytes. These data types store data on a row-overflow data page. A LOB also encompasses data types that store data on dedicated LOB page structures, which use a text or an image pointer of in-row references to LOB data pages. For more information about data storage, see the Pages and extents architecture guide.
The bit manipulation functions operate on the tinyint, smallint, int, bigint, binary(n), and varbinary(n) data types. Large object (LOB) data types, such as varchar(max), nvarchar(max), varbinary(max), image, ntext, text, xml, and common language runtime (CLR) BLOB types, aren't supported.
Examples
A. Calculate the BIT_COUNT in a binary value
In the following example, the number of bits set to 1 in a binary value are calculated.
SELECT BIT_COUNT(0xabcdef) AS Count;
The result is 17. This is because 0xabcdef in binary is 1010 1011 1100 1101 1110 1111, and there are 17 bits with a value set to 1.
B. Calculate the BIT_COUNT in an integer
In the following example, the number of bits set to 1 in an integer are calculated.
SELECT BIT_COUNT(17) AS Count;
The result is 2. This is because 17 in binary is 0001 0001, and there are only 2 bits with a value set to 1.