The <frequency-percentage> CSS data type represents a value that can be either a <frequency> or a <percentage>. Frequency values, e.g. the pitch of a speaking voice, are not currently used in any CSS properties.


The value of a <frequency-percentage> is either a <frequency> or a <percentage>; see their individual reference pages for details about their syntaxes.


Use in calc()

Where a <frequency-percentage> is specified as an allowable type, this means that the percentage resolves to a frequency and therefore can be used in a calc() expression.

Formal syntax

<frequency-percentage> = 
<frequency> |


Valid percentage values

90% Positive percentage
+90% Positive percentage with leading +
-90% Negative percentage — not valid for all properties that use percentages

Invalid percentage values

90 % No space is allowed between the number and the unit

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>.


CSS Values and Units Module Level 4
# mixed-percentages

Browser compatibility

BCD tables only load in the browser

See also