The below HTML file should help you in testing out the Bootstrap grid system

Testing Bootstrap Grid System

<!-- 
	Markup for testing Bootstrap grid system
	1. On extra small devices, viewport width <768px, all of the div's below should stack upon each other
	2. On small devices, viewport width ≥768px, div's should show up 2 per row
	3. On medium devices, viewport width ≥992px, 3 div's in 1st row, and 1 in 2nd row should show up
	4. On large devices, viewport width ≥1200px, all 4 div's should show up in single row
-->

<div class="row grid-testing">
	<div class="col-xs-12 col-sm-6 col-md-4 col-lg-3">
		.col-xs-12 .col-sm-6 .col-md-4 .col-lg-3
	</div>
	<div class="col-xs-12 col-sm-6 col-md-4 col-lg-3">
		.col-xs-12 .col-sm-6 .col-md-4 .col-lg-3
	</div>
	<div class="col-xs-12 col-sm-6 col-md-4 col-lg-3">
		.col-xs-12 .col-sm-6 .col-md-4 .col-lg-3
	</div>
	<div class="col-xs-12 col-sm-6 col-md-4 col-lg-3">
		.col-xs-12 .col-sm-6 .col-md-4 .col-lg-3
	</div>
</div>