crispy-css/scss/functions/_units.scss

/**
 * functions to convert px to em and rem
 *
 *
 * @author Björn Hase
 *
 */

$base__font-size: 16px !default;

/**
 * calculate pixel value to em
 *
 * @param  {px} $fontSize
 * @return {em}
 */
@function pxToEm($font-size) {
    @return ($font-size / $base__font-size) * 1em;
}

/**
 * calculate px value to rem
 *
 * @param  {px} $fonz-size
 * @param  {px} $font-size
 * @return {em}
 */
@function pxToRem($font-size) {
    @return ($font-size / $base__font-size) * 1rem;
}