<div class="container">
<div class="row">
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 1</p></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 2</p></div>
<div class="clearfix visible-sm-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 3</p></div>
<div class="clearfix visible-md-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 4</p></div>
<div class="clearfix visible-sm-block"></div>
<div class="clearfix visible-lg-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 5</p></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 6</p></div>
<div class="clearfix visible-sm-block"></div>
<div class="clearfix visible-md-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 7</p></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 8</p></div>
<div class="clearfix visible-sm-block"></div>
<div class="clearfix visible-lg-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 9</p></div>
<div class="clearfix visible-md-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 10</p></div>
<div class="clearfix visible-sm-block"></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 11</p></div>
<div class="col-sm-6 col-md-4 col-lg-3"><p>Box 12</p></div>
</div>
</div>
Correct not in every row
should you have a total of 12 columns?
<div class="container">
<div class="row">
<div class="col-sm-6"><p>Box 1</p></div>
<div class="col-sm-6"><p>Box 2</p></div>
</div>
<div class="row">
<div class="col-sm-6"><p>Box 3</p></div>
<div class="col-sm-6"><p>Box 4</p></div>
</div>
</div>
I followed this example: link