Using the CSS calc() function

DanielAugust 11, 2021August 12, 2021

The calc() is a CSS function that lets you calculate values right in your CSS. For example:

.main-content {
  width: calc(100% - 40px);
}

One of the most useful features of this function is that you can mix multiple CSS units. In our example, we used a percentage with pixels. Bun we can also use units like em, pt, rem, etc.

In 90% of the cases, I find myself using calc with the substractions sign, but you can use it along with:

• additions by using +
• subtractions by using -
• multiplication by using *
• division using by /

The operator must be wrapped in white spaces. Some operators don't work well if you don't have a white a before and after it.

// use this code 
.logo {
  height: calc(4rem - 30px);
}
// instead of this one
.logo {
  height: calc(4rem-30px);
}

It is supported in all major browsers https://caniuse.com/#feat=calc.

Using calc() with CSS variables and SASS

It works out of the box with the new CSS variables:

--text-input-width: 500px;
max-width: calc(var(--text-input-width) / 2);

Using calc() in SASS or SCSS

For SASS variables you will have to interpolate the value in the calc() function:

$body_padding}: 20px;
 height: calc(100% - #{$body_padding})