Generated by SassMeister.com.

input.scss

$total: 7;

@function col-width($col, $total){
    @return percentage($col/$total);
}

.col-1{
    width: col-width($col:1, $total:7);
}

.col-2{
    width: col-width($col:2, $total:7);
}

.col-4{
    width: col-width($col:4, $total:7);
}

output.css

.col-1 {
  width: 14.2857142857%;
}

.col-2 {
  width: 28.5714285714%;
}

.col-4 {
  width: 57.1428571429%;
}