SQL BIT_LENGTH

What does SQL BIT_LENGTH do?

BIT_LENGTH returns the length of a string or binary value in bits.

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Compatible dialects for SQL BIT_LENGTH:

SQL BIT_LENGTH Full Explanation

BIT_LENGTH is a scalar string function defined in the SQL standard. It evaluates its single argument and returns an integer that represents how many bits are required to store that value. Because one byte equals eight bits, the result is OCTET_LENGTH(expression) * 8. If the argument is NULL, the function returns NULL. The function works on character strings (CHAR, VARCHAR, TEXT) and binary strings (BLOB, BYTEA, VARBINARY) without changing their content. In multibyte encodings, BIT_LENGTH still counts physical storage bytes, not characters, so a UTF-8 string containing non-ASCII symbols will yield more bits than its visible length. BIT_LENGTH does not trim trailing spaces. Precision of the result is implementation-dependent but generally fits in a standard INTEGER.

SQL BIT_LENGTH Syntax

BIT_LENGTH ( expression );

SQL BIT_LENGTH Parameters

Example Queries Using SQL BIT_LENGTH

-- Basic usage with ASCII text
SELECT BIT_LENGTH('ABC');

-- Multibyte UTF-8 text
SELECT BIT_LENGTH('ƒøø');

-- Binary column example (PostgreSQL BYTEA)
SELECT id, BIT_LENGTH(file_data) AS size_bits
FROM uploads
ORDER BY size_bits DESC
LIMIT 5;

Expected Output Using SQL BIT_LENGTH

Each query returns an integer: 24 for 'ABC' (3 bytes x 8 bits), 72 for 'ƒøø' (9 bytes x 8 bits in UTF-8), and the last example lists the bit size of each upload record

Use Cases with SQL BIT_LENGTH

Quickly determine storage size for auditing or compression analysis
Validate that encoded values fit within transport limits
Compare raw versus compressed sizes in ETL workflows
Build metrics such as average blob size (in bits) per record

Common Mistakes with SQL BIT_LENGTH

Assuming BIT_LENGTH counts characters rather than bytes – it counts bytes * 8
Forgetting that multibyte encodings inflate the result
Expecting support in all databases – SQL Server, Oracle, and SQLite do not implement BIT_LENGTH natively
Using BIT_LENGTH on numeric or date types without casting to a string first

First Introduced In

SQL-92 standard; first implemented in early PostgreSQL releases.

Frequently Asked Questions

What data types can BIT_LENGTH accept?

BIT_LENGTH works on any character or binary string type. Cast other data types to TEXT or BLOB before using it.

Does BIT_LENGTH include trailing spaces?

Yes. The function measures the raw storage length, so trailing spaces in CHAR values count toward the result.

How can I emulate BIT_LENGTH in SQL Server?

Use DATALENGTH(expression) * 8 to obtain the bit length.

Why is the result larger than the visible characters?

In multibyte encodings such as UTF-8, some characters occupy more than one byte. BIT_LENGTH counts every byte, so the bit length exceeds the character count.