The <frequency> CSS data type represents a frequency dimension, such as the pitch of a speaking voice. It is not currently used in any CSS properties.


The <frequency> data type consists of a <number> followed by one of the units listed below. As with all CSS dimensions, there is no space between the unit literal and the number.


Represents a frequency in hertz. Examples: 0Hz, 1500Hz, 10000Hz.
Represents a frequency in kilohertz. Examples: 0kHz, 1.5kHz, 10kHz.

Note: Although the number 0 is always the same regardless of unit, the unit may not be omitted. In other words, 0 is invalid and does not represent 0Hz or 0kHz. Though the units are case-insensitive, it is good practice to use a capital "H" for Hz and kHz, as specified in the SI.


Valid frequency values

12Hz     Positive integer
4.3Hz    Non-integer
14KhZ    The unit is case-insensitive, though non-SI capitalization is not recommended.
+0Hz     Zero, with a leading + and a unit
-0kHz    Zero, with a leading - and a unit

Invalid frequency values

12.0     This is a <number>, not an <frequency>, because it is missing a unit.
7 Hz     No space is allowed between the number and the unit.
0        Although unitless zero is an allowable <length>, it's an invalid <frequency>.


Specification Status Comment
CSS Values and Units Module Level 3
The definition of '<frequency>' in that specification.
Candidate Recommendation Initial definition.

Note: This data type was initially introduced in CSS Level 2 for the now-obsolete aural media type, where it was used to define the pitch of the voice. However, the <frequency> data type has been reintroduced in CSS3, though no CSS property is using it at the moment.

Browser compatibility

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See also