sample of Sass responsive grid

gistfile1.sass

@for $i from 1 through 4 {
  .span#{$i} {
    margin:0;
    padding:0;
    float:left;

    @media (min-width:960px) {
      width: percentage(1/$i);
    }
    @media (max-width:780px) and (max-width:959px) {
      @if $i == 1 or $i == 4 {
        width:100%;
      }
      @else {
        width:50%;
      }
    }
    @media (max-width:779px) {
      width:100%;
    }
  }
}