round()
Experimental: This is an experimental technology
Check the Browser compatibility table carefully before using this in production.
The round()
CSS function returns a rounded number based on a selected rounding strategy.
Authors should use a custom CSS property (e.g., --my-property
) for the rounding value, interval, or both; using the round()
function is redundant if these have known values.
Syntax
css
width: round(var(--width), 50px);
width: round(up, 101px, var(--interval));
width: round(down, var(--height), var(--interval));
margin: round(to-zero, -105px, 10px);
Parameter
The round(<rounding-strategy>, valueToRound, roundingInterval)
function specifies an optional rounding strategy, a value (or mathematical expression) to be rounded and a rounding interval (or mathematical expression).
The valueToRound
is rounded according to the rounding strategy, to the nearest integer multiple of roundingInterval
.
<rounding-strategy>
-
The rounding strategy. This may be one of the following values:
up
-
Round
valueToRound
up to the nearest integer multiple ofroundingInterval
(if the value is negative, it will become "more positive"). This is equivalent to the JavaScriptMath.ceil()
method. down
-
Round
valueToRound
down to the nearest integer multiple ofroundingInterval
(if the value is negative, it will become "more negative"). This is equivalent to the JavaScriptMath.floor()
method. nearest
(default)-
Round
valueToRound
to the nearest integer multiple ofroundingInterval
, which may be either above or below the value. If thevalueToRound
is half way between the rounding targets above and below (neither is "nearest"), it will be rounded up. Equivalent to JavaScriptMath.round()
. to-zero
-
Round
valueToRound
to the nearest integer multiple ofroundingInterval
closer to/towards zero (a positive number will decrease, while a negative value will become "less negative"). This is equivalent to the JavaScriptMath.trunc()
method.
valueToRound
-
The value to be rounded. This must be a
<number>
,<dimension>
, or<percentage>
, or a mathematical expression that resolves to one of those values. roundingInterval
-
The rounding interval. This is a
<number>
,<dimension>
, or<percentage>
, or a mathematical expression that resolves to one of those values.
Return value
The value of valueToRound
, rounded to the nearest lower or higher integer multiple of roundingInterval
, depending on the rounding strategy
.
- If
roundingInterval
is 0, the result isNaN
. - If
valueToRound
androundingInterval
are bothinfinite
, the result isNaN
. - If
valueToRound
is infinite butroundingInterval
is finite, the result is the sameinfinity
. - If
valueToRound
is finite butroundingInterval
is infinite, the result depends on the rounding strategy and the sign ofA
:up
- IfvalueToRound
is positive (not zero), return+∞
. IfvalueToRound
is0⁺
, return0⁺
. Otherwise, return0⁻
.down
- IfvalueToRound
is negative (not zero), return−∞
. IfvalueToRound
is0⁻
, return0⁻
. Otherwise, return0⁺
.nearest
,to-zero
- IfvalueToRound
is positive or0⁺
, return0⁺
. Otherwise, return0⁻
.
- The argument calculations can resolve to
<number>
,<dimension>
, or<percentage>
, but must have the same type, or else the function is invalid; the result will have the same type as the arguments. - If
valueToRound
is exactly equal to an integer multiple ofroundingInterval
,round()
resolves tovalueToRound
exactly (preserving whethervalueToRound
is0⁻
or0⁺
, if relevant). Otherwise, there are two integer multiples ofroundingInterval
that are potentially "closest" tovalueToRound
, lowerroundingInterval
which is closer to−∞
and upperroundingInterval
which is closer to+∞
.
Formal syntax
<round()> =
round( <rounding-strategy>? , <calc-sum> , <calc-sum> )
<rounding-strategy> =
nearest |
up |
down |
to-zero
<calc-sum> =
<calc-product> [ [ '+' | '-' ] <calc-product> ]*
<calc-product> =
<calc-value> [ [ '*' | '/' ] <calc-value> ]*
<calc-value> =
<number> |
<dimension> |
<percentage> |
<calc-constant> |
( <calc-sum> )
<calc-constant> =
e |
pi |
infinity |
-infinity |
NaN
Examples
Round positive values
This example demonstrates how the round()
function's rounding strategies work for positive values.
Of the five boxes below, the round()
function is used to set the height of the last four.
The value to be rounded is between 100 px and 125 px in each case, and the rounding value is 25px in all cases.
The height of the boxes is therefore either rounded up to 125 px or down to 100 px.
HTML
The HTML defines 5 div
elements that will be rendered as boxes by the CSS.
The elements contain text indicating the rounding strategy, initial value, and expected final height of the box (in brackets).
html
<div class="box box-1">height: 100px</div>
<div class="box box-2">up 101px (125px)</div>
<div class="box box-3">down 122px (100px)</div>
<div class="box box-4">to-zero 120px (100px)</div>
<div class="box box-5">nearest 117px (125px)</div>
CSS
The CSS that is applied to all boxes is shown below.
Note that we apply a custom CSS property named --rounding-interval
, that we will use for the rounding interval.
css
div.box {
width: 100px;
height: 100px;
background: lightblue;
padding: 5px;
--rounding-interval: 25px;
}
The first div
from the left isn't targeted with specific CSS rules, so it will have a default height of 100px.
The CSS for div
two, three, and four is shown below, which round, up, down, and to-zero, respectively.
css
div.box-2 {
height: round(up, 101px, var(--rounding-interval));
}
div.box-3 {
height: round(down, 122px, var(--rounding-interval));
}
div.box-4 {
height: round(to-zero, 120px, var(--rounding-interval));
}
Notice how above we indicate the rounding interval using var()
and the custom CSS property --rounding-interval
.
The last box is set without specifying a rounding strategy, and hence defaults to nearest
.
In this case, the nearest interval to 117 px is 125px, so it will round up.
Just for contrast, here we specified hard coded values for both the rounding value and interval.
While this is allowed, you wouldn't do this normally because there is no point rounding a number when you already know what the result must be.
css
div.box-5 {
height: round(117px, 25px);
}
Result
If the browser supports the CSS round()
function, you should see five columns with heights that are rounded as indicated by their contained text.
Specifications
Specification |
---|
CSS Values and Units Module Level 4 # funcdef-round |
Browser compatibility
BCD tables only load in the browser