rem() is a Sass mixin that converts pixel values to rem values for whatever property is passed to it.

rem.scss

/*
 * 'rem' is a Sass mixin that converts pixel values to rem values for whatever property is passed to it.
 * It returns two lines of code — one of the regular pixel values (for IE), and another with the
 * converted rem values (for everyone else). Special thanks to Chris Epstein (http://chriseppstein.github.com)
 * and Martin Bavio (http://martinbavio.com) for the help and code!
 * 
 * Sample input:
 * .element {
 *   @include rem('padding',10px 0 2px 5px);
 * }
 * 
 * Sample output:
 * .element {
 *   padding: 10px 0 2px 5px;
 *   padding: 1rem 0 0.2rem 0.5rem;
 * }
 * 
 */

// Baseline, measured in pixels
// The value should be the same as the font-size value for the html element
// If the html element's font-size is set to 62.5% (of the browser's default font-size of 16px),
// then the variable below would be 10px.
$baseline_px: 10px;

@mixin rem($property, $px_values) {

	// Convert the baseline into rems
	$baseline_rem: ($baseline_px / 1rem);

	// Print the first line in pixel values
	#{$property}: $px_values;

	// If there is only one (numeric) value, return the property/value line for it.
	@if type-of($px_values) == 'number' {
		#{$property}: $px_values / $baseline_rem;
	}

	// If there is more than one value, create a list and perform equations on each value
	@else {

		// Create an empty list that we can dump values into
		$rem_values: ();

		@each $value in $px_values {

			// If the value is zero, return 0
			@if $value == 0 { 
				$rem_values: append($rem_values, $value); 
			}

			// If the value is not zero, convert it from px to rem
			@else {
				$rem_values: append($rem_values, ($value / $baseline_rem) );
			}

		}

		// Return the property and its list of converted values
		#{$property}: $rem_values;

	}

}

Please turn this into a "full on" Git repo so I can help you improve and maintain this. :) I like the idea of using rem units with a fallback for px. I never fully embraced ems because of the inability to control the compounding issue, so using rem is certainly on my radar.

Your wish has been granted. https://github.com/bitmanic/rem. Thanks for your interest, and for any future improvements you make to the code. Enjoy!

Good find... I added another if for 'auto' statements:

@else if $value == 'auto' {
    $rem_values: append($rem_values, $value);
}

Getting an error now, what is a fix for this?

The result of 0px == 0 will be false in future releases of Sass.
Unitless numbers will no longer be equal to the same numbers with units.

I'm in the same boat as CoplanConsulting ^ above.