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<frequency>

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.

Syntax

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.

Units

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

Examples

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 allowed for <length>s, it's invalid for <frequency>s.

Specifications

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

Feature	Chrome	Firefox (Gecko)	Internet Explorer	Opera	Safari
Basic support	No support	No support	No support	No support^[1]	No support

Feature	Android	Firefox Mobile (Gecko)	IE Mobile	Opera Mobile	Safari Mobile
Basic support	No support	No support	No support	No support	No support

[1] Some versions of Opera may have (partial) support for the obsolete aural media group, and through the pitch property support for the <frequency> data type.

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https://developer.mozilla.org/en-US/docs/Web/CSS/frequency