Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.4)
// Compass (v1.0.1)
// ----

$px-only: true;
$pixelBase : 16; /* 1 */
$visual-grid-breakpoints: '';
$grid-columns: 12;

@mixin media($query:$feature $value $columns, $total-columns: $grid-columns) {
  @if length($query) == 1 {
    @media screen and ($default-feature: nth($query, 1)) {
      $default-grid-columns: $grid-columns;
      $grid-columns: $total-columns !global;
      @content;
      $grid-columns: $default-grid-columns !global;
    }
  }

  @else {
    $loopTo: length($query);
    $mediaQuery: 'screen and ';
    $default-grid-columns: $grid-columns;
    $grid-columns: $total-columns !global;

    @if length($query) % 2 != 0 {
      $grid-columns: nth($query, $loopTo) !global;
      $loopTo: $loopTo - 1;
    }

    $i: 1;
    @while $i <= $loopTo {
      $mediaQuery: $mediaQuery + '(' + nth($query, $i) + ': ' + nth($query, $i + 1) + ') ';

      @if ($i + 1) != $loopTo {
        $mediaQuery: $mediaQuery + 'and ';
      }

      $i: $i + 2;
    }

    @media #{$mediaQuery} {
      @content;
      $grid-columns: $default-grid-columns !global;
    }
  }
}

@function new-breakpoint($query:$feature $value $columns, $total-columns: $grid-columns) {
  @if length($query) == 1 {
    $query: $default-feature nth($query, 1) $total-columns;
  }

  @else if length($query) % 2 == 0 {
    $query: append($query, $total-columns);
  }

  @if not belongs-to($query, $visual-grid-breakpoints) {
    $visual-grid-breakpoints: append($visual-grid-breakpoints, $query, comma) !global;
  }

  @return $query;
}

@function parseInt($n) {
	@return $n / ($n * 0 + 1); /* 2 */
}

@function u($values){ /* 3 */

  $list: (); /* 4 */

  @each $value in $values { /* 5 */

    $unit : unit($value); /* 6 */
    $val  : parseInt($value); /* 2 */

    @if ($px-only) and ($unit == 'rem') { /* 7 */
          $list: append($list, ($val * $pixelBase) + px); /* 7 */
    }

    @else if($unit == 'px') or ($unit == 'rem'){ /* 8 */
          $list: append($list, $value); /* 8 */
    }

    @else {
          @warn 'There is no unit conversion for #{$unit}'; /* 9 */
    }

  }

  @return $list(); /* 10 */
}

$desktopW: u(120rem); // reffers to desktop container size 120rem ie 1200px
$desktop: new-breakpoint(min-width $desktopW 12); // this is breakpoint for desktops

body {
  width: 100%;
  @include media($desktop) {
    width:  $desktopW;
  }
}

SassMeister-output.css

/* 1 */
body {
  width: 100%;
}
@media screen and (min-width: 1920px) {
  body {
    width: 1920px;
  }
}