How to center content in a Bootstrap column?

I am trying to center column's content. Does not look like it works for me. Here is my HTML:

<div class="row">
   <div class="col-xs-1 center-block">
       <span>aaaaaaaaaaaaaaaaaaaaaaaaaaa</span>
   </div>
 </div>

JSFiddle Demo

Use:

<!-- unsupported by HTML5 -->
<div class="col-xs-1" align="center">

instead of

<div class="col-xs-1 center-block">

You can also use bootstrap 3 css:

<!-- recommended method -->
<div class="col-xs-1 text-center">

Bootstrap 4 now has flex classes that will center the content:

<div class="d-flex justify-content-center">
   <div>some content</div>
</div>

Note that by default it will be x-axis unless flex-direction is column

[Updated Dec 2020]: Tested and Included 5.0 version of Bootstrap.

I know this question is old. And the question did not mentioned which version of Bootstrap he was using. So i'll assume the answer to this question is resolved.

If any of you (like me) stumbled upon this question and looking for answer using current bootstrap 5.0 (2020) and 4.5 (2019) framework, then here's the solution.

Bootstrap 4.5 and 5.0

Use d-flex justify-content-center on your column div. This will center everything inside that column.

<div class="row">
    <div class="col-4 d-flex justify-content-center">
        // Image
    </div>
</div>

If you want to align the text inside the col just use text-center

<div class="row">
    <div class="col-4 text-center">
        // text only
    </div>
</div>

If you have text and image inside the column, you need to use d-flex justify-content-center and text-center.

<div class="row">
    <div class="col-4 d-flex justify-content-center text-center">
        // for image and text
    </div>
</div>

Bootstrap naming conventions carry styles of their own, col-XS-1 refers to a column being 8.33% of the containing element wide. Your text, would most likely expand far beyond the specified width, and couldn't possible be centered within it. If you wanted it to constrain to the div, you could use something like css word-break.

For centering the content within an element large enough to expand beyond the text, you have two options.

Option 1: HTML Center Tag

<div class="row">
  <div class="col-xs-1 center-block">
    <center>
      <span>aaaaaaaaaaaaaaaaaaaaaaaaaaa</span>
    </center>
  </div>
</div>

Option 2: CSS Text-Align

<div class="row">
  <div class="col-xs-1 center-block" style="text-align:center;">
    <span>aaaaaaaaaaaaaaaaaaaaaaaaaaa</span>
  </div>
</div>

If you wanted everything to constrain to the width of the column

<div class="row">
  <div class="col-xs-1 center-block" style="text-align:center;word-break:break-all;">
    <span>aaaaaaaaaaaaaaaaaaaaaaaaaaa</span>
  </div>
</div>

UPDATE - Using Bootstrap's text-center class

<div class="row">
  <div class="col-xs-1 center-block text-center">
    <span>aaaaaaaaaaaaaaaaaaaaaaaaaaa</span>
  </div>
</div>

FlexBox Method

<div class="row">
  <div class="flexBox" style="
    display: flex;
    flex-flow: row wrap;
    justify-content: center;">
    <span>aaaaaaaaaaaaaaaaaaaaaaaaaaa</span>
  </div>
</div>

http://jsfiddle.net/usth0kd2/13/

Bootstrap 4/Bootstrap 5, horizontal and vertical align contents using flex box

<div class="page-hero d-flex align-items-center justify-content-center">
 <h1>Some text </h1>
</div>

Use bootstrap class align-items-center and justify-content-center

.page-hero {
  height: 200px;
  background-color: grey;
}

<link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css" integrity="sha384-MCw98/SFnGE8fJT3GXwEOngsV7Zt27NXFoaoApmYm81iuXoPkFOJwJ8ERdknLPMO" crossorigin="anonymous">

<div class="page-hero d-flex align-items-center justify-content-center">
  <h1>Some text </h1>
</div>