get-multiplier() & strip-units() bonus. For setting line-height and EM values, specifically for vertical rhythms. This is different from the px to em functions out there.

get-multiplier.sass

// strip-units()
//   Remove units from a Sass value with units (em, px, etc.)
//     http://stackoverflow.com/questions/12328259/how-do-you-strip-the-unit-from-any-number-in-sass#answer-12335841
//   EXAMPLE
//     strip-units($my-var);
@function strip-units($number) {
  @return $number / ($number * 0 + 1);
}


// get-multiplier()
//   Get the multiplier for the pixel value divided by the current/contextual font size
//   Requires $vertical-rhythm-base variable to be set, should be unitless
//   EXAMPLE
//     get-multiplier(24, $font-size-h4);
@function get-multiplier($px-value, $current-font-size) {
  @return ($px-value / strip-units($current-font-size * $vertical-rhythm-base));
  // EXAMPLE 30px /            (    3em               *          16px        )
  //         30px /                                  48px
  //                        = .625
}


// USAGE
$vertical-rhythm-base: 16; // 16px, should be unitless
$font-size-base: 1em;      // 1em = 16px base font size (set by browser)
$font-size-h1: $font-size-base *2; // 32px

h1 {
  font-size: $font-size-h1;

  // get the 48px muplitplier value with the h1 font size context as EMs
  line-height:    get-multiplier(48, $font-size-h1); // line heights should be unitless: http://www.w3.org/wiki/CSS/Properties/line-height#Description

  // get the 16px multiplier value with the h1 font size context as EMs
  padding-bottom: get-multiplier(16, $font-size-h1) +em;
}


// PROCESSED
h1 {
  font-size: 2em;       // 32px
  line-height: 1.5;     // 48px
  padding-bottom: .5em; // 16px
}