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Using the CSS calc() function

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

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})