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* a small mixin for easy use of rem with px as fallback
* usage: @include x-rem(font-size, 14px)
* usage: @include x-rem(marign, 0 12px 2 1.2)
* usage: @include x-rem(padding, 1.5 24px)
* thanks to Eric Meyer for
* and Hans Christian Reinl for
@mixin x-rem($property, $values) {
// Create a couple of empty lists as output buffers.
$base-font-size: 16px; // should be consistent with your html/body font-size
$px-values: ();
$rem-values: ();
// Loop through the $values list
@each $value in $values {
// For each property value, if it's in rem or px, derive both rem and
// px values for it and add those to the end of the appropriate buffer.
// Ensure all pixel values are rounded to the nearest pixel.
@if $value == 0 or $value == 0px {
// 0 -- use it without a unit
$px-values: join($px-values, 0);
$rem-values: join($rem-values, 0);
} @else if type-of($value) == number and not unitless($value) and (unit($value) == px) {
// px value given - calculate rem value from base-font-size
$new-rem-value: $value / $base-font-size;
$px-values: join($px-values, round($value));
$rem-values: join($rem-values, #{$new-rem-value}rem);
} @else {
// unitless value - use those directly as rem and calculate the px-fallback
$px-values: join($px-values, round($value * $base-font-size));
$rem-values: join($rem-values, #{$value}rem);
// output the converted rules
#{$property}: $px-values;
#{$property}: $rem-values;

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commented Feb 25, 2013

Thanks for the rem mixin - super helpful for my current project.

I added:
@else if $value == auto {
// auto - don't add px or rem
$px-values: join($px-values, auto);
$rem-values: join($rem-values, auto);

to allow for auto values.


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commented Jan 23, 2014

@steffen and @caleb, how about:

@else if $value == auto or $value == inherit {
    // auto or inherit - don't add px or rem
    $px-values: join($px-values, $value);
    $rem-values: join($rem-values, $value);
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