PX to EM with Sass

Whenever I used to write CSS I whipped out a px-em calculator to help my pixel-thinking brain write proper-em-values. After having been introduced to Sass and Compass, this is thankfully a thing of the past.

Sass lets you define variables to hold the values you use a lot.

$base-font-size: 20px;

html {
    font-size: $base-font-size;

Sass also lets you define functions, which can take parameters and even default parameters to set values.

@function em($px, $base: $base-font-size) {
    @return ($px / $base) * 1em;

All you have to do is give this function whatever pixel value you would normally have converted manually.

.title {
    font-size: em(37px);

Since em values are relative its tag’s parent, you need to keep changes to the current size when nesting.

.fine-print {
    $font-size: 10px;
    font-size: em($font-size);
    .title {
        font-size: em(10px, $font-size);

The Sass documentation has some more information on functions if you feel like diving in.