Data Type Storage Requirements

The following tables indicate the approximate data storage requirements for each data type.

Numeric Data Types

Data Type	Storage Requirement
TINYINT	1 byte
SMALLINT	2 bytes
MEDIUMINT	3 bytes
INT	4 bytes
BIGINT	8 bytes
FLOAT(p)	4 bytes if p <= 24, otherwise 8 bytes
DOUBLE	8 bytes
DECIMAL	See table below
BIT(M)	(M+7)/8 bytes

Note that MEDIUMINT columns will require 4 bytes in memory (for example, in InnoDB buffer pool).

Decimal

Decimals are stored using a binary format, with the integer and the fraction stored separately. Each nine-digit multiple requires 4 bytes, followed by a number of bytes for whatever remains, as follows:

Remaining digits	Storage Requirement
0	0 bytes
1	1 byte
2	1 byte
3	2 bytes
4	2 bytes
5	3 bytes
6	3 bytes
7	4 bytes
8	4 bytes

String Data Types

In the descriptions below, M is the declared column length (in characters or in bytes), while len is the actual length in bytes of the value.

Data Type	Storage Requirement
ENUM	1 byte for up to 255 enum values, 2 bytes for 256 to 65,535 enum values
CHAR(M)	M × w bytes, where w is the number of bytes required for the maximum-length character in the character set
BINARY(M)	M bytes
VARCHAR(M), VARBINARY(M)	len + 1 bytes if column is 0 – 255 bytes, len + 2 bytes if column may require more than 255 bytes
TINYBLOB, TINYTEXT	len + 1 bytes
BLOB, TEXT	len + 2 bytes
MEDIUMBLOB, MEDIUMTEXT	len + 3 bytes
LONGBLOB, LONGTEXT	len + 4 bytes
SET	Given M members of the set, (M+7)/8 bytes, rounded up to 1, 2, 3, 4, or 8 bytes
INET6	16 bytes
UUID	16 bytes

In some character sets, not all characters use the same number of bytes. utf8 encodes characters with one to three bytes per character, while utf8mb4 requires one to four bytes per character.

When using field the COMPRESSED attribute, 1 byte is reserved for metadata. For example, VARCHAR(255) will use +2 bytes instead of +1.

Examples

Assuming a single-byte character-set:

Value	CHAR(2)	Storage Required	VARCHAR(2)	Storage Required
''	' '	2 bytes	''	1 byte
'1'	'1 '	2 bytes	'1'	2 bytes
'12'	'12'	2 bytes	'12'	3 bytes

Date and Time Data Types

Data Type	Storage Requirement
DATE	3 bytes
TIME	3 bytes
DATETIME	8 bytes
TIMESTAMP	4 bytes
YEAR	1 byte

Microseconds

MariaDB 5.3 and MySQL 5.6 introduced microseconds. The underlying storage implementations were different, but from MariaDB 10.1, MariaDB defaults to the MySQL format (by means of the mysql56_temporal_format variable). Microseconds have the following additional storage requirements:

MySQL 5.6+ and MariaDB 10.1+

Precision	Storage Requirement
0	0 bytes
1,2	1 byte
3,4	2 bytes
5,6	3 bytes

MariaDB 5.3 - MariaDB 10.0

Precision	Storage Requirement
0	0 bytes
1,2	1 byte
3,4,5	2 bytes
6	3 bytes

NULLs

For the InnoDB COMPACT, DYNAMIC and COMPRESSED row formats, a number of bytes will be allocated in the record header for the nullable fields. If there are between 1 and 8 nullable fields, 1 such byte will be allocated. In the record payload area, no space will be reserved for values that are NULL.

For the InnoDB REDUNDANT row format, the overhead is 1 bit in the record header (as a part of the 1-byte or 2-byte "end of field" pointer). In that format, a NULL fixed-length field will consume the same amount of space as any NOT NULL value in the record payload area. The motivation is that it is possible to update in place between NOT NULL and NULL values.

In other formats, NULL values usually require 1 bit in the data file, 1 byte in the index file.

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