CSS <frequency> Data Type

The CSS <frequency> data type represents a frequency value. It consists of a number followed by either the Hz or kHz unit and is used by CSS features that accept frequency-based values.

Syntax

A <frequency> value consists of a <number> immediately followed by a frequency unit:

<frequency> = <number>Hz | <number>kHz

Examples of frequency values include:

440Hz
1000Hz
1kHz
2.5kHz

There must not be a space between the number and the unit.

Frequency Units

CSS provides two units for representing frequency values:

Unit	Name	Description
`Hz`	Hertz	Represents one cycle per second.
`kHz`	Kilohertz	Represents 1,000 cycles per second.

CSS units are ASCII case-insensitive, so forms such as Hz, hz, and HZ are equivalent. The conventional forms Hz and kHz are generally used for readability.

Converting Frequency Units

One kilohertz is equal to 1,000 hertz. Values expressed with either unit can therefore represent the same frequency:

1kHz = 1000Hz
1.5kHz = 1500Hz
0.5kHz = 500Hz

Zero Values

A frequency of zero can be written with a frequency unit, such as 0Hz or 0kHz. When a CSS grammar requires a <frequency>, a unit should be included because a unitless 0 is a <number>, not a <frequency>.

0Hz
0kHz

<frequency> Examples

The following values are examples of valid CSS frequencies:

Value	Equivalent Frequency
`440Hz`	440 hertz
`1kHz`	1,000 hertz
`2.5kHz`	2,500 hertz
`0.25kHz`	250 hertz

The <frequency> data type is primarily a unit and syntax definition, so its usefulness depends on a CSS feature that accepts frequency values.

Specifications

The <frequency> data type and its units are defined in the CSS Values and Units Module Level 4 .