Bootstrap is set up on a 12 grid system by default, but you can change this if you wish.
At 1800 pixels, you’d be in the
.col-lg- group as it covers everything ≥1200px.
So if you had a design that had two columns, one that was 2/3 of the width and one that was 1/3 the width at 1200px+, you’d use something like this:
<div class="col-lg-8"> ... your content here for 2/3 width </div> <div class="col-lg-4"> ... your content here for 1/3 width </div>
8/12 = 2/3
4/12 = 1/3
Note – this will only affect (in Bootstrap 3) viewports larger than 1200px. If it’s below that, they’ll just stack on top of each other. So adding more grid classes helps you get through various content break points when things start to look weird.
Complete example: http://getbootstrap.com/css/#grid-example-mixed-complete