Display Divs One Below The Other

I have a parent div which is 100% width and 500px height. Now I want to put multiple divs of same size width:250px; height:80px one below the other and once it crosses the height

Solution 1:

You need CSS column layout. Something like this:

#parent {
    width: 100%;
    height: 500px;
    background: #eee;

    -moz-column-count: 3;
    -moz-column-gap: 20px;
    -webkit-column-count: 3;
    -webkit-column-gap: 20px;
}
#parent .box {
    width: 250px;
    height: 80px;
    background: #AAA;
    margin-bottom: 10px;
    display: inline-block;
}

Demo: http://jsfiddle.net/J8A24/

Support: browser support chart.
Further reading: Multiple Columns

For IE you may want to use one of the many polyfills or leave it as is, inline-blocks will gracefully degrade for IE.

Solution 2:

Achievable with some PHP (untested):

<div style="width:100%;height:500px;position:relative;">
  <div class="innerContainer" style="float:left;width:250px;">
    <div class="innerDiv" style="height:80px;">
      <?php for($i = 1; $i < $numDivs; $i++) : ?>
        <?php if($i % 6 == 0) : ?>
          <!-- create new container div -->
          </div>
          <div class="innerContainer" style="float:left;width:250px;">
        <?php endif; ?>
        <!-- put stuff in child div here -->
      <?php endfor; ?>
    </div>
  </div>
</div>

Or you can use CSS columns as mentioned in the other answer, but I'm used to dealing with things that have to be widely supported in old browsers.