# calc()

## BaselineWidely available

This feature is well established and works across many devices and browser versions. It’s been available across browsers since July 2015.

The `calc()` CSS function lets you perform calculations when specifying CSS property values. It can be used with `<length>`, `<frequency>`, `<angle>`, `<time>`, `<percentage>`, `<number>`, `<integer>`, and `<color-function>` values.

## Syntax

css
``````/* calc(expression) */
calc(100% - 80px)

/* Expression with a CSS function */
calc(100px * sin(pi / 2))

/* Expression containing a variable */
calc(var(--hue) + 180)

/* Expression with color channels in relative colors */
lch(from aquamarine l c calc(h + 180))
``````

The `calc()` function takes a single expression as its parameter, and the expression's result is used as the value for a CSS property. In this expression, the operands can be combined using the operators listed below. When the expression contains multiple operands, `calc()` uses the standard operator precedence rules:

`+`

`-`

Subtracts the second operand from the first operand.

`*`

Multiplies the specified operands.

`/`

Divides the left-side operand (dividend) by the right-side operand (divisor).

All operands, except those of type `<number>`, must be suffixed with an appropriate unit string, such as `px`, `em`, or `%`. You can use a different unit with each operand in your expression. You may also use parentheses to establish computation order when needed.

## Description

There's a few points to keep in mind about `calc()`:

• Serializing the arguments inside `calc()` follows the IEEE-754 standard for floating point math, which means there's a few cases to be aware of regarding the `infinity` and `NaN` constants. For more details on how constants are serialized, see the `calc-keyword` page.
• Math expressions involving percentages for widths and heights on table columns, table column groups, table rows, table row groups, and table cells in both auto and fixed layout tables may be treated as if `auto` is specified.
• The `calc()` function cannot directly substitute the numeric value for percentage types; for instance `calc(100 / 4)%` is invalid, while `calc(100% / 4)` is valid.
• When `calc()` is used where an `<integer>` is expected, the value will be rounded to the nearest integer. So, `calc(1.4)` will result in a value of `1`. If the fractional part of the value is exactly `0.5`, the value will be rounded up. For example, `calc(1.5)` will result in a value of `2`, while `calc(-1.5)` will round to `-1`.

### Rules and best practices while using `calc()`

• The `+` and `-` operators must be surrounded by whitespace. For instance, `calc(50% -8px)` will be parsed as "a percentage followed by a negative length" — which is an invalid expression — while `calc(50% - 8px)` is "a percentage followed by a subtraction operator and a length". Likewise, `calc(8px + -50%)` is treated as "a length followed by an addition operator and a negative percentage".
• The `*` and `/` operators do not require whitespace, but adding it for consistency is recommended.
• It is permitted to nest `calc()` functions, in which case, the inner ones are treated as simple parentheses.
• For lengths, you can't use `0` to mean `0px` (or another length unit); instead, you must use the version with the unit: `margin-top: calc(0px + 20px);` is valid, while `margin-top: calc(0 + 20px);` is invalid.
• Current implementations require that for the `*` and `/` operators, one of the operands has to be unitless. For `/`, the right operand must be unitless. For example `font-size: calc(1.25rem / 1.25)` is valid but `font-size: calc(1.25rem / 125%)` is invalid.

### Support for computing color channels in relative colors

The `calc()` function can be used to manipulate color channels directly within the context of relative colors. This allows for dynamic adjustments of color channels in color models such as `rgb()`, `hsl()`, and `lch()`.

The relative color syntax defines a number of color-channel keywords, each of which represents the value of the color channel as a `<number>` (see Channel values resolve to `<number>` values for more information). The `calc()` function can use these color-channel keywords to perform dynamic adjustments on the color channels, for example, `calc(r + 10)`.

## Formal syntax

`<calc()> =   calc( <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        `

## Accessibility

When `calc()` is used for controlling text size, be sure that one of the values includes a relative length unit, for example:

css
``````h1 {
font-size: calc(1.5rem + 3vw);
}
``````

This ensures that text size will scale if the page is zoomed.

## Examples

### Positioning an object on screen with a margin

`calc()` makes it easy to position an object with a set margin. In this example, the CSS creates a banner that stretches across the window, with a 40-pixel gap between both sides of the banner and the edges of the window:

css
``````.banner {
position: absolute;
left: 40px;
width: calc(100% - 80px);
border: solid black 1px;
background-color: yellow;
text-align: center;
box-sizing: border-box;
}
``````
html
``````<div class="banner">This is a banner!</div>
``````

### Automatically sizing form fields to fit their container

Another use case for `calc()` is to help ensure that form fields fit in the available space, without extruding past the edge of their container, while maintaining an appropriate margin.

Let's look at some CSS:

css
``````input {
display: block;
width: calc(100% - 1em);
}

#form-box {
width: calc(100% / 6);
border: 1px solid black;
}
``````

Here, the form itself is established to use 1/6 of the available window width. Then, to ensure that input fields retain an appropriate size, we use `calc()` again to establish that they should be the width of their container minus 1em. Then, the following HTML makes use of this CSS:

html
``````<form>
<div id="form-box">
<label for="misc">Type something:</label>
<input type="text" id="misc" name="misc" />
</div>
</form>
``````

### Nesting with CSS variables

You can use `calc()` with CSS variables. Consider the following code:

css
``````.foo {
--widthA: 100px;
--widthB: calc(var(--widthA) / 2);
--widthC: calc(var(--widthB) / 2);
width: var(--widthC);
}
``````

After all variables are expanded, `widthC`'s value will be `calc(calc(100px / 2) / 2)`. When it's assigned to `.foo`'s width property, all inner `calc()` functions (no matter how deeply nested) will be flattened to just parentheses. Therefore, the `width` property's value will eventually be `calc((100px / 2) / 2)`, which equals `25px`. In short, a `calc()` inside of a `calc()` is identical to using parentheses.

### Adjusting color channels in relative colors

The `calc()` function can be used to adjust individual color channels in relative colors without the need for storing color channel values as variables.

In the example below, the first paragraph uses a `<named-color>`. In the paragraphs that follow, `calc()` is used with the `rgb()` and `hsl()` functions to adjust the values of each color channel relative to the original named color.

html
``````<p class="original">Original text color in rebeccapurple</p>
<p class="increase-hue">Hue increased by 80</p>
<p class="increase-lightness">Lightness increased by 20</p>
<p class="decrease-lightness">Lightness decreased by 10</p>
``````
css
``````.original {
color: rebeccapurple;
}

.increase-hue {
color: lch(from rebeccapurple l c calc(h + 80));
}

.increase-lightness {
color: lch(from rebeccapurple calc(l + 20) c h);
}

.decrease-lightness {
color: lch(from rebeccapurple calc(l - 10) c h);
}
``````

For another example of using the `calc()` function to derive relative colors, see the Using math functions section on the Using relative colors page.

## Specifications

Specification
CSS Values and Units Module Level 4
# calc-func

## Browser compatibility

BCD tables only load in the browser