Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.4.9)
// Compass (v1.0.1)
// ----

$grid-granularity: 4 !default;
$widths: ();

@for $i from 1 through $grid-granularity {
  @for $j from 1 through $i {
    $newWidth: unquote('.col-#{$j}-#{$i}');
    $width: $j/$i;
    
    @if (map-has-key($widths, $width)) {
      $newWidth: append(map-get($widths, $width), $newWidth, comma);
    } @else {
      $newWidth: $newWidth;
    }
    $widths: map-merge($widths, ($width: $newWidth));
  }
}

@each $grid-granularity in $widths {
  $key: nth($grid-granularity, 1);
  $value: nth($grid-granularity, 2);
  
  #{$value} {
    width: $key * 100%;
  }
}

SassMeister-output.css

.col-1-1, .col-2-2, .col-3-3, .col-4-4 {
  width: 100%;
}

.col-1-2, .col-2-4 {
  width: 50%;
}

.col-1-3 {
  width: 33.33333%;
}

.col-2-3 {
  width: 66.66667%;
}

.col-1-4 {
  width: 25%;
}

.col-3-4 {
  width: 75%;
}