px-to-rem.scss

$base-font-size: 16;

// strips away any unit from a value: e.g. "16px" => 16
@function strip-unit($number) {
  @if type-of($number) == 'number' and not unitless($number) {
    @return $number / ($number * 0 + 1);
  }

  @return $number;
}

@function px-to-rem($size, $base: $base-font-size) {
  $pxUnitless: strip-unit($size);
  
  @return #{$pxUnitless / $base}rem;
}

.some-selector {
  font-size: px-to-rem(20);
  padding: px-to-rem(14) px-to-rem(32);
}