PostgreSQL has a bit_length() function that returns the number of bits in a given string. We pass the string as an argument and the function returns the number of bits in that string.

Example

Here’s an example to demonstrate:

SELECT bit_length('a');

Result:

8

Here’s another example with various string lengths:

SELECT 
    bit_length('Cat') AS "Cat",
    bit_length('Cafe') AS "Cafe",
    bit_length('Café') AS "Café",
    bit_length('คาเฟ่') AS "คาเฟ่";

Result:

 Cat | Cafe | Café | คาเฟ่ 
-----+------+------+------
  24 |   32 |   40 |  120

bit_length() vs octet_length()

The bit_length() function returns the number of bits in the string, whereas octet_length() returns the number of bytes. Therefore, the result of the bit_length() function is eight times the length returned by the octet_length() function (which returns the number of bytes in the string).

Here they are compared:

SELECT 
    'bit_length()' AS "Function",
    bit_length('Cat') AS "Cat",
    bit_length('Cafe') AS "Cafe",
    bit_length('Café') AS "Café",
    bit_length('คาเฟ่') AS "คาเฟ่"
UNION
SELECT 
    'octet_length()',
    octet_length('Cat') AS "Cat",
    octet_length('Cafe') AS "Cafe",
    octet_length('Café') AS "Café",
    octet_length('คาเฟ่') AS "คาเฟ่";

Result:

    Function    | Cat | Cafe | Café | คาเฟ่ 
----------------+-----+------+------+------
 bit_length()   |  24 |   32 |   40 |  120
 octet_length() |   3 |    4 |    5 |   15

Passing a Null Argument

Passing a null argument results in null:

SELECT bit_length(null);

Result:

 bit_length 
------------
       null