The CSS calc() function


While this tutorial has content that we believe is of great benefit to our community, we have not yet tested or edited it to ensure you have an error-free learning experience. It's on our list, and we're working on it! You can help us out by using the "report an issue" button at the bottom of the tutorial.

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

.pirate {
  position: absolute;
  /* lets have the pirate 20px from the left */
  left: calc(50px - 30px);

At first glance you might think Why the heck would I care? I can just set it to 20px. Well things get interesting when you realize that you can mix and match the units:

left: calc(1.5em - 8px);

And things get even more interesting when you mix in percentage values. The following sets to width of the selected element to 80px less than 100%:

width: calc(100% - 80px);

Make sure to use spaces around the operand. For example: v1 + v2, not v1 +v2 or v1+v2.

You can use calc() anywhere where you would use numeric values (e.g.: width, max-height, margin-left, …)

Calc() is very useful for things like vertical centering if you know the height of the element you want to center. You just add a margin-top to the element of 50% of the viewport height minus half the height of the element. Let’s say our element is 100px tall:

.my-element {
  /* 50vh = 50% viewport height */
  margin-top: calc( 50vh - 50px );
  width: 200px;
  height: 50px;

Browser Support

Can I Use calc? Data on support for the calc feature across the major browsers from caniuse.com.

Creative Commons License