rem()

Limited availability

This feature is not Baseline because it does not work in some of the most widely-used browsers.

The rem() CSS function returns a remainder left over when the first parameter is divided by the second parameter, similar to the JavaScript remainder operator (%). The remainder is the value left over when one operand, the dividend, is divided by a second operand, the divisor. It always takes the sign of the dividend.

For example, the CSS rem(27, 5) function returns the remainder of 2. When dividing 27 by 5, the result is 5 with a remainder of 2. The full calculation is 27 / 5 = 5 * 5 + 2.

Syntax

css
/* Unitless <number> */
line-height: rem(21, 2); /* 1 */
line-height: rem(14, 5); /* 4 */
line-height: rem(5.5, 2); /* 1.5 */

/* Unit based <percentage> and <dimension> */
margin: rem(14%, 3%); /* 2% */
margin: rem(18px, 5px); /* 3px */
margin: rem(10rem, 6rem); /* 4rem */
margin: rem(26vmin, 7vmin); /* 5vmin */
margin: rem(1000px, 29rem); /* 72px - if root font-size is 16px */

/* Negative/positive values */
rotate: rem(200deg, 30deg); /* 20deg */
rotate: rem(140deg, -90deg); /* 50deg */
rotate: rem(-90deg, 20deg); /* -10deg */
rotate: rem(-55deg, -15deg); /* -10deg */

/* Calculations */
scale: rem(10 * 2, 1.7); /* 1.3 */
rotate: rem(10turn, 18turn / 3); /* 4turn */
transition-duration: rem(20s / 2, 3000ms * 2); /* 4s */

Parameter

The rem(dividend, divisor) function accepts two comma-separated values as its parameters. Both parameters must have the same type, number, dimension, or <percentage>, for the function to be valid. While the units in the two parameters don't need to be the same, they do need of the same dimension type, such as <length>, <angle>, <time>, or <frequency> to be valid.

dividend

A calculation that resolves to a <number>, <dimension>, or <percentage> representing the dividend.

divisor

A calculation that resolves to a <number>, <dimension>, or <percentage> representing the divisor.

Return value

Returns a <number>, <dimension>, or <percentage> (corresponds to the parameters' type) representing the remainder, that is, the operation left over.

  • If divisor is 0, the result is NaN.
  • If dividend is infinite, the result is NaN.
  • If dividend is positive the result is positive (0⁺), and if dividend is negative the result is negative (0⁻).

Formal syntax

<rem()> = 
  rem( <calc-sum> , <calc-sum> )  

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | '/' ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

Specifications

Specification
CSS Values and Units Module Level 4
# funcdef-rem

Browser compatibility

Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
rem()

See also