A Sass function to convert px values into rems, based on the px to em function in Bourbon (http://bourbon.io/docs/#px-to-em)

_rem.scss

// Convert a px value into a rem value.
// Supply the rem value to the primary style sheet and the px fallback to the ltie9 style sheet.

@function rem($pxval) {
    
    $val: strip-unit($pxval);
    $base: strip-unit($browser-default-font-size);
    
    @if ($ltie9 == true) {
        @return $val * 1px;
    }
    
    @else {
        @return ($val / $base) * 1rem;
    }
}