An example grid system using Sass mixins.

grid.scss

// Config
$container-width: 96% !default;
$container-max-width: 1200px !default;
$grid-base-outer-width: 940 !default;
$grid-base-col-width: 60 !default;
$grid-base-gutter-width: 20 !default;
$grid-cols: 12 !default;


// Clearfix
@mixin clearfix {

  &:before,
  &:after {
    content: " ";
    display: table;
  }

  &:after {
    clear: both;
  }
}


// Container
@mixin container {
  @include clearfix;
  width: $container-width;
  max-width: $container-max-width;
  margin: 0 auto;
}


// Row
@mixin row {
  @include clearfix;
}


// Grid columns
$grid-col-width: percentage($grid-base-col-width / $grid-base-outer-width);
$grid-gutter-width: percentage($grid-base-gutter-width / $grid-base-outer-width);

@mixin span-columns($cols) {
  float: left;
  width: ($grid-col-width + $grid-gutter-width) * $cols - $grid-gutter-width;
  margin-right: $grid-gutter-width;

  &:last-child {
    margin-right: 0;
  }
}


// Clears last column of row
@mixin omega($nth) {

  &:nth-child(#{$nth}) {
    margin-right: 0;
  }
}


// Reset row
@mixin omega-reset($nth) {

  &:nth-child(#{nth}) {
    margin-right: $grid-gutter-width;
  }
}