You would have to create your own styles if you are unwilling to use the answer posted here: Half columns in Twitter Bootstrap 3
If you look at Bootstrap, you'll see there is little mystery to how it works. For example:
.col-sm-5 {
width: 41.66666667%;
}
Since bootstrap is (usually) a 12 column grid, you can see that the math is straightforward: 5 / 12 = 41.6666667%.
So, you would just write your OWN styles, and do the math: 1.5 / 12 = 12.5%;
Bootstrap 3 sizes:
// Note, you can't use a dot in the middle, so separate with underscore or dash
.col-xs-1_5 {
width: 12.5%;
}
@media(min-width:768px){
.col-sm-1_5 {
width: 12.5%;
}
}
@media(min-width:992px){
.col-md-1_5 {
width: 12.5%;
}
}
@media(min-width:1200px){
.col-lg-1_5 {
width: 12.5%;
}
}
Do not modify the bootstrap css file. Put the above styles into your own css file.