col-xs-12 col-sm-4 col-md-4 col-lg-4

CSS
 <div class="row">
  <div class="col-sm-4">.col-sm-4</div>
  <div class="col-sm-4">.col-sm-4</div>
  <div class="col-sm-4">.col-sm-4</div>
</div> 
Source

Also in CSS: